Formulas

Section 3.7

Formula

•A formula is an equation that relates two or more real-life quantities.

•Don’t Write--You can solve a formula to describe one quantity in terms of the

others.

Using the Distance Formula

In other words SOLVE FOR r

d=rt

d = rt

Find a formula for r in terms of d and t.

d rt

tt

dr

t

Now Use the new formula to find the rate if you drive 400 miles for 5.5 hours. (nearest tenth)

dr

t

400 miles

5.5 hoursr

72.7 mi

rhr

Using an Area Formula

In other words SOLVE FOR l

A=lw

A = lw

Find a formula for l in terms of A and w.

lwA

ww

lw

A

Now Use the new formula to find the length of a rectangle with an area of 35ft2 and a width of 7 ft.

lw

A

lft

ft

7

35 2

lft 5

Simple Interest

Pt

t

Pt

I Pr

tI PrSolve for r.

What is my rate for an investment of $1500 if it made $54 in interest for one year?

rPt

I

54

(1500)(1)r

.036 r 3.6%

1. L = V - WH

2.

3.

4.

The formula for the volume of a rectangular prism is V = LWH. Which

equation solves the formula for L?

LV H

W

LV W

H

LV

HW

1. h = 3Vb

2.

3.

4.

The formula for the volume of a pyramid is V = . Which equation

solves the formula for h?

1

3bh

h 3b

V

h 3V

b

h V

3b

Solving a function for y…

43 yx Rewrite the equation so

that you isolate the y

variable

-3x -3x

xy 34

Solve for y: 4x – 2y = 12

1. Subtract 4x from both sides

2. Simplify

3. Divide both sides by -2

4. Does it simplify?

- 4x - 4x

-2y = –4x+12

-2 -2

y = 2x - 6

Practice… Solve for y

2 5

2 10

5 3 8 2

x y

x y

y x x

2 5

2 10

8

5

y x

x y

xy