# Linear law question

• Oct 19th 2012, 04:01 AM
Thorpelizts
Linear law question
The first attachment shows the question I need to ask. So, I've drawn the graph, but don't know how to do part b, which is to find a and b, the value of x when y=20x^2 and the volume of the cuboid. Also, for c, how to draw y=x^3, as in terms of the scale, it would reach quite a large number so how do I put I down?Thx
• Oct 19th 2012, 06:49 PM
chiro
Re: Linear law question
Hey Thorpelizts.

For your graph recall that the gradient (which is your a) is given by the change in y over a change in x.

So since you have a straight line you can get this by looking at some interval (say between 1 and 2) and then look at the difference between in the y values for x = 1 and x = 2. Your a value (which is also called the gradient) will be (y2 - y1)/(x2 - x1) where y2 is the y value for x = x2 and y1 is the y value for x = x1.

Now for the b: b actually represents the y-intercept.

If you have an equation y = mx + b and you let x = 0, you get y = b which is the value when the function crosses the y-axis (which is why this is called the y-intercept).

So if you look at where the graph crosses the y-axis, this is your b value.
• Oct 19th 2012, 09:32 PM
Thorpelizts
Re: Linear law question
What abt part c? About the scale?