







Travelling in opposite directions 
20151206 

Roselyn pose la question : Jenny and Mark commute to work, travelling in opposite directions. Jenny leaves the house at 8 AM, and averages 35 kph. Mark leaves at 8:15 AM, and averages 40 kph.At what time will they be 40 kilometers apart? Penny Nom lui répond. 





The derivative of x^1/3 
20151108 

omar pose la question : hi can help me
am teacher ask me about x^1/3 Derivation definition . Penny Nom lui répond. 





The train fares are proportional to the square root of distance traveled 
20140111 

manish pose la question : train fares are proportional to the sq .root of distance traveled. the train fare is Rs. 24.4 for a distance of 140 kms. by how much % does the total fare increase if the same distance is covered by breaking the journey after every 35 kms. Penny Nom lui répond. 





When would one flip the inequality sign? 
20140109 

Natasha pose la question : Would one flip the inequality symbol in this equation: (explain why)
(9a)/(9) > 81
And please explain in what circumstances one would flip the inequality sign
THANKS! Penny Nom lui répond. 





If 4 cooks can bake 8 pies in 6 hours????? 
20130318 

Kenneth pose la question : Hello:
I want to determine which quantities are directly and inversely proportional in order to determine the answer for the following:.
If 4 cooks can bake 8 pies in 6 hours, 2 cooks can bake how many pies in 4 hours?
Answer: 2 2/3 pies
Can someone fully explain what I need to know in order to determine what is directly and inversely proportional in the example above?
I thank you for your reply. Robert Dawson lui répond. 





If x ix directly proportional to y then ... 
20120219 

Crystal pose la question : I understand that we say x and y are proportional, then y = kx.
Generally when we say x is proportional to y, we think that when x increases y increases.
Now I am questioning whether that is actually true.
If k is negative, then when x increases, y DECREASES.
My question is does this mean this statement is incorrect:
If x is proportional to y, when x increases, y increases proportionally.
Is it more correct to say:
If x is proportional to y, when x increases, y either increases proportionally or decreases proportionally.
Along the same line of reasoning, when x is inversely proportional to y,
we think that when x increases y decreases, but that is true only if k is positive.
Is that correct? Harley Weston lui répond. 





The derivative of f(x) = (x+1)^1/2 
20110905 

Carla pose la question : Find the derivative using the limit process of
f(x) = (x+1)^1/2 Harley Weston lui répond. 





I need to make $1000 profit 
20110328 

Kat pose la question : I need to make $1000 profit selling plants for $3 each. My direct cost is $2 per plant and my overhead is $5oo. How many pots (plants = 1 per pot) do I need to make $1000? Penny Nom lui répond. 





Using the limit definition 
20100606 

Meagan pose la question : Using the limit definition find the derivative of 3/(2x^2) Harley Weston lui répond. 





The adjacency matrix of an undirected graph 
20100115 

Bhavya pose la question : Let Cn be the undirected graph with vertex set V = {1,2,3,...,n} and edge set E = {(1,2), (2,3), (3,4),.... , (n1,n), (n,1)}. Let An be the adjacency matrix of Cn.
a. Find the determinant of An.
b. Find (An)^2 Robert Dawson lui répond. 





Proportionality 
20091103 

Nazrul pose la question : If x is proportional to y , how can I prove that (x^2y^2) is proportional to xy.
Please explain the process. Penny Nom lui répond. 





Proportionality 
20090629 

Nazrul pose la question : If x is proportional to y and y is proportional to z , how can I prove that (x^2+y^2)^3/2 is proportional to z^3 Harley Weston lui répond. 





Direct and inverse relationships 
20090406 

allison pose la question : A piece of string is cut into n pieces of equal lengths L
(1) does n vary directly or inversely with L Penny Nom lui répond. 





Direct, inverse and indirect proportionality 
20090304 

Brian pose la question : My 14 year old is confused about indirectly proportional and inversely proportional. On searching on the internet we were directed to:
http://mathcentral.uregina.ca/QQ/database/QQ.09.00/ellis1.html
Here leanne starts explaining indirectly proportional and ends up describing inversely proportional. Has Leanne got it wrong ?
What is indirectly proportional.
Thanks
Brian Chris Fisher lui répond. 





The parabola with vertex (7,2) and directrix y = 3 
20090121 

Deann pose la question : Find an equation of the parabola with vetrex (7,2) and directrix y =(3) Penny Nom lui répond. 





y varies jointly as x and the square of z and... 
20090105 

peter pose la question : I don't really get the terms in this problem. Could you explain it: If y varies jointly as x and the square of z and inversely as the cube of w, by what factor is y increased when z is doubled and w is divided by 3 and x remains the same? Harley Weston lui répond. 





The flight of an airplane 
20080829 

kobina pose la question : You are traveling on an airplane that is moving at 500 mph in a direction 40deg north of west.Therefore , You are travelling (due to the plane ) at how many mph toward the west. Stephen La Rocque lui répond. 





A force vector 
20080828 

moumita pose la question : F=20N...this force is acting along a vector A=4j+3k.what is F? Penny Nom lui répond. 





What angle should he turn? 
20071201 

Jasmine pose la question : Bob is traveling due north he then turns left 45 degrees followed by four 20 degree turns to the right
What is his new heading if he needed to turn so his heading was SSW what direction and what angle should he turn? Walter Whiteley lui répond. 





Direct and inverse variations 
20071127 

Julie pose la question : Please Help I do not understand this question. X varies directly as the square of S and inversely as T. How does X change when S is doubled ? When both S and T are doubled ? I appreciate your help with this problem. Stephen La Rocque lui répond. 





Variation 
20071029 

deeqa pose la question : 1. A car traveled 175mi at a certain speed. If the speed had been 20mph faster,
the trip could have been made in 1hr less time. Find the speed
2. The average weekly allowance A of children varies directly as their grade level, G.
If the average allowance of an 8thgrade student is $8.56 per week, what is the average
weekly allowance of a 5thgrade
The time T required to do a job varies inversely as the number of people P working. It takes 2hr for 4
working. It takes 2 hrs for 4 volunteers to distribute flyers to a neighborhood. How long would it take 12
volunteers to complete the job? Penny Nom lui répond. 





Direct variation 
20071007 

Kimberly pose la question : If y is directly proportional to the square of x,
and x=2 when y=12, then what is the value of y when x=3? Penny Nom lui répond. 





The derivative of f(x)=1/(x1) 
20070921 

Michelle pose la question : im having trouble finding the derivative of f(x)=1/(x1) using the f(x+h)f(x)/h method. Stephen La Rocque lui répond. 





Direct variation 
20070507 

Jennifer pose la question : assume that y varies directly as x. find y when x = 54 if y =1/4 when x=3/2 Stephen La Rocque lui répond. 





Direct and inverse Variation 
20070403 

liz pose la question : how do you tell if an equation varies Directly or Inversely? ex.
x= 2y or
xy+12=3
i know that if you have three numbers (x. y, z) that it varies jointly but how do you tell if it is Inverse or Direct?
Thanks for the Help!
liz Stephen La Rocque lui répond. 





What is the intensity 5m below the surface? 
20070331 

david pose la question : I have this question which I am supposed to set it up and solve as a differential equation. I know how to solve the diffrential equation but I am having hard time understanding this question. Here is the question: The intensity of light in the ocean decreases the deeper you dive. In fact, the rate at which the intensity decreases is proportional to the current intensity. Setup the corresponding differential equation and solve for I(Y), the intensity I as a function of current intensity Y. If the light intensity 2m below the surface is 25% of the intensity at the surface, what is the intensity 5m below the surface. Can you please explain to me what does it mean by current intensity and how do I set this equation up. Thanks for the help. Penny Nom lui répond. 





Direct and inverse variation 
20070303 

Rene pose la question : Hi I'm Rene, I'm stuck with some problems in direct and inverse variation.
I know how to solve direct and inverse problems when only one variation is in a question at a time.
EX: p varies inversely as the square root of q, and when p=12, q=36 find p when q=16
12*6 =p*4 72=4p 18=p
But how would you solve a problem like.....
If s varies directly as r and inversely as t, and s=10 when r=5 and t=3, for what value of t will s=3 when r=4 ? Penny Nom lui répond. 





What is the diameter of the planet? 
20061207 

Niall pose la question : In April 2005, scientists claimed to have captured light from an extrasolar planet orbiting a brown dwarf in the constellation Hydra some 230 lightyears from Earth. The scientists believe the planet is about five times the mass of Jupiter.
Assume the planet has the same density as Jupiter. What is the diameter of the planet? Stephen La Rocque lui répond. 





Direct variation 
20061105 

Johann pose la question : The perimeter of regular octagon varies directly with the length of one side of the octagon Stephen La Rocque lui répond. 





Direct and Inverse variation 
20061027 

Vishalinee pose la question :
i'm not sure how to use the words direct variation and inverse variation to describe thre relationship between: a. speed and distance b.speed and time c. distance and time. and then i need to create equations using the descriptions. i am really messed up with direct and inverse variation. Karen McIver lui répond. 





livinia the housefly finds herself caught in the oven 
20060627 

Danielle pose la question :
livinia the housefly finds herself caught in the oven at the point (0,0,1). the temperature at the points in the oven is given by the function
T(x,y,z) = 10 (xe^{(y2)} + ze^{(x2)})
where the units are in degrees celsius.
(i.)so if livinia begins to move towards the point (2,3,1) at what rate in deg/cm does she find the temp. changing?
(ii.)in what direction should she move in order to cool off as rapidly as possible?
(iii.)suppose that livinia can fly at a speed of the square root of 2 (cm/sec.) if she moves in the direction of part (ii) at what rate will she find the temp. to be changing?
Penny Nom lui répond. 





Equations of two lines 
20060405 

Wael pose la question : Determine a cartesian equation of the line passing through A and V as a direction vector?
1 A (2;1) and V = j
2 A (2;3) and V = i Penny Nom lui répond. 





A proof by contraposition 
20060316 

Eban pose la question :
1)by mathematical induction prove that 1^{2} + 3^{2 }+ 5^{2 }+ ...... + (2k1)^{2} = (1/3)k(2k1)(2k+1) for all positive integers k.
2)show that the contrapositive of the following statement is true. if 1 + M^{7} is even, then M is odd.
Stephen La Rocque lui répond. 





The equation of an ellipse 
20050717 

Allan pose la question : I working on a problem that asks me to give the equation of an ellipse when only the location of the directrix and the length of the latus rectum are given. No other points on the ellipse are given. Again, the only "givens" are:
Length of latus rectum = 12
Location of directrix is x = 16
If I could determine the eccentricity, I could proceed from there by taking the ratio of the distance from a focus to the latus rectum point to the distance of the point from the directrix, but I lack the x coordinate of c. I've searched the text, and feel I've "missed something" somewhere! I note that the latus rectum segment is unique in one respect in that it is parallel to the directrix, where any other line segment on the ellipse to the focus would not be. Please indicate where I'm going wrong. Chris Fisher lui répond. 





Direct and inverse variation 
20041005 

Abraham pose la question : Given that y varies inversely as x and x varies directly as z.If z is doubled then y is halved.Why is that true.Please explain.I'm having trouble understanding the different types of variation Penny Nom lui répond. 





X is due north of Y ... 
20040811 

A student pose la question : X is due north of Y and 2km distant. Z is due east of Y and has a bearing of S35°12'E from X. How far, to the nearest metre, is Z from X? Penny Nom lui répond. 





A linear function 
20020909 

Chad pose la question : If y = 9x  13 does it represent a linear function? And if it does what is its slope and is it a direct variation? Peny Nom lui répond. 





Why do you flip the inequality sign? 
20011026 

Sean pose la question : I have a question about an inequality problem. Here it is: Solve and graph 5  3x => 17. (=> is greater than or equal). Please tell me why you flip the inequality sign when divinding by a negative number. Penny Nom lui répond. 





Proportionality: direct and indirect 
20010118 

Nancy Ellis pose la question : What is the difference between directly proportional and indirectly proportional? Leeanne Boehm lui répond. 





Direct and inverse variation 
20001212 

Ashley pose la question : I'm stuck on this unit of direct and inverse variation..please and my problems and show me how to do each PLEASE!!! Assume that y varies directly as x If y= 4 when x = 2, find y when x= 6 Assume that y varies inversely as x If y =4 when x=2, find y when x =6 Penny Nom lui répond. 





Reversing the direction of an inequality. 
19990306 

Mallory White pose la question : If the Problem was 4a plus 5 is less than or equal to 14, why would you change the sign to greater than or equal to? Jack LeSage and Harley Weston lui répond. 





Parabolas 
19980724 

Danica pose la question : how do you find the focus, vertex, and directrix of 4xy^22y33=0 Penny Nom lui répond. 





The twodigit numbers from 1099 
19980121 

Alexis Riddle pose la question : My name is Alexis. I'm a student in 8th grade and I'm taking Algebra I Honors. My question is: In a string of numbers, two adjacent digits are considered as a twodigit number. For instance, the string 11012 contains the numbers 10, 11, and 12. What is the number of digits in the smallest string that contains all of the twodigit numbers from 1099? Please help and thank you for any assistance you can give me. Penny Nom lui répond. 





Parabolic Mirrors 
19970128 

Megan Wennberg pose la question : Consider a ray of light that passes through a chord of a parabola (the chord is above the focus and parallel to the directrix), hits the parabola at a point (x,y) and is reflected through the focus. If d1 is the distance from the chord to the point of incidence (x,y) and d2 is the distance from (x,y) to the focus, can you prove that the sum of the distances d1+d2 is constant, independent of the particular point of incidence. Penny Nom lui répond. 

