Transcript Formulas and Functions

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
Find a formula for r in terms of d and t.
d  rt
In other words SOLVE FOR r
d=rt
d = rt
t
t
d
r
t
Now Use the new
formula to find the
rate if you drive 400
miles for 5.5 hours.
(nearest tenth)
d
r
t
400 miles
r
5.5 hours
mi
72.7
r
hr
Using an Area Formula
Find a formula for l in terms of A and w.
A  lw
In other words SOLVE FOR l
A=lw
A = lw
w w
A
l
w
Now Use the new
formula to find the
length of a
rectangle with an
area of 35ft2 and a
width of 7 ft.
A
l
w
35 ft 2
l
7 ft
5 ft  l
Simple Interest
I  Pr t
Solve for r.
I
Pr t

Pt
Pt
I
r
Pt
What is my rate for an
investment of $1500 if it made
$54 in interest for one year?
54
r
(1500)(1)
.036  r
3.6%
The formula for the volume of a rectangular
prism is V = LWH. Which equation solves the
formula for L?
1.
2.
3.
4.
L = V - WH
VH
L
W
VW
L
H
V
L
HW
The formula for the volume of a pyramid
is V = 1 bh . Which equation solves the
3
formula for h?
1.
2.
3.
4.
h = 3Vb
3b
h
V
3V
h
b
V
h
3b
Solving a function for y…
3x  y  4
-3x
-3x
y  4  3x
Rewrite the
equation so
that you
isolate the y
variable
Solve for y:
1. Subtract 4x from
both sides
2. Simplify
3. Divide both sides
by -2
4. Does it simplify?
4x – 2y = 12
- 4x
- 4x
-2y = –4x+12
-2
-2
y = 2x - 6
Practice… Solve for y
2x  y  5
y  2 x  5
2 x   y  10
2 x  10  y
5 y  3x  8  2 x
8 x
y
5