# MPM1D Rearranging Formulas (Equations) 2016-04-14

We worked on rearranging formulas today. This is different than what we’ve done before because a formula will contain more than one variable. It shows a relationship between variables.

For example, we’re all familiar with the formula for the area of a rectangle:

$A=l \times w$

where $A$ is area, $l$ is length, and $w$ is width. This formula is used to calculate the area when you know the length and the width.

However, sometimes we know area and want to calculate either length or width. For example, suppose I want to find out the length of a rectangle if its area is 100 and its width is 20. I can rearrange my formula:

$\frac{A}{w} = \frac{l \times w}{w}$

$latex \frac{A}{w} = l$

Now I have a formula for length, and I can substitute:

$l = \frac{100}{20}$

$l = 5$

We practiced rearranging a bunch of formulas for different variables:

$A = \frac{bh}{2}$

$a = \frac{x+y}{2}$

$latex V = lwh$

$C = \pi d$

Your homework tonight was slightly (and accidentally!) different. I gave you a page with problems that included formulas. You didn’t have to rearrange (sorry, that’s what I meant to do!), but instead you just had to evaluate each one.

We’ll practise rearranging some more stuff tomorrow.