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 March 29th, 2014, 07:00 AM #1 Newbie   Joined: Mar 2014 From: London Posts: 2 Thanks: 0 Really need your help with these questions guys!!!! 1. Z is proportional to X. When X = -4, Z = 2. Enter the value of X required to give Z = -2. 2. Y is proportional to X. When X = 2, Y = 1. Find the value of X required to give Y = -4. 3. Z is proportional to (X - 2). When X = 1, Z = 1. Enter the value of X required to give Z = -2. 4. Y is proportional to (1 - X). When X = 2, Y = -2. Find the value of X required to give Y = 6. 5. Y is inversely proportional to X. When X = 2, Y = 1. Find the value of X required to give Y = 6. [Express your as a decimal correct to 2sf] 6.C is inversely proportional to A^2. When A = 0.1, C = 50. Find C when A = .02. This might help =IMPORTANT NOTE In the following, x^2, x^3, mean "x squared", "x cubed", respectively. Generally, a^n means "a to the power n".
 March 29th, 2014, 07:12 AM #2 Senior Member     Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs I'll show you how to do the first, and then see if you can do the rest in like manner. 1. Z is proportional to X. When X = -4, Z = 2. Enter the value of X required to give Z = -2. The first statement means we may write: $Z=kX$ Using the given data, we may then write: $2=k(-4)$ Solving for k, we find: $k=-\frac{1}{2}$ And so the relationship between Z and X is: $Z=-\frac{1}{2}X$ Now, we let Z = -2 and solve for X: $-2=-\frac{1}{2}X$ $X=4$
March 29th, 2014, 07:13 AM   #3
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 Originally Posted by taytay100 1. Z is proportional to X. When X = -4, Z = 2. Enter the value of X required to give Z = -2. 2. Y is proportional to X. When X = 2, Y = 1. Find the value of X required to give Y = -4. 3. Z is proportional to (X - 2). When X = 1, Z = 1. Enter the value of X required to give Z = -2. 4. Y is proportional to (1 - X). When X = 2, Y = -2. Find the value of X required to give Y = 6. 5. Y is inversely proportional to X. When X = 2, Y = 1. Find the value of X required to give Y = 6. [Express your as a decimal correct to 2sf] 6.C is inversely proportional to A^2. When A = 0.1, C = 50. Find C when A = .02. This might help =IMPORTANT NOTE In the following, x^2, x^3, mean "x squared", "x cubed", respectively. Generally, a^n means "a to the power n".
There are two different types of proportions, direct and inverse. Direct means simply as it sounds; as one increases (or decreases,) the other does the same at the same rate. On the flip side of the coin, inverse proportion means that as one decreases, the other increases at the same rate (and vice versa.)

I will give you the equations for each proportion and see if you can go from there:

Direct Proportion: y = kx
Inverse proportion: y = k/x
With Squares: y = kx^2 OR in your case since it's inversely proportional: C = K/A^2

Just as a hint, you have to find K first before making the proportion.

To make things simple, the following link describes in great detail how to go about these kinds of problems. If you need more specific help, let us know.

Directly Proportional and Inversely Proportional

Last edited by Harbinger; March 29th, 2014 at 07:19 AM.

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### is this an inverse proportion 0.1 x =5/y inverse proportion

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