Page 188 - Algebra 1

Example
4
Application: Geometry
The formula for the circumference of a circle is C = 2πr. If the circle’s circumference is 24 inches, what is the radius? Leave the symbol π in the answer.
SOLUTION
Step1: Sincethequestionaskedfortheradius,thefirststepistosolvethe formula for r.
C = 2πr C =2πr
__ 2π 2π
_C=r 2π
Step2:
_2 4 = r 2π
_12=r π
Isolatethevariabler. Simplify.
Substitute24forC.
Simplify.
The radius of the circle is _12 inches.
Application: Travel Plans
The Ramirez family is taking a trip to the coast. They live 270 miles
from the coast. They want to make the trip in 4_1 hours. Use the distance 2
formula d = rt to determine the average speed the family needs to drive. SOLUTION
Step1: Theanswerwillbethespeedtheyaredriving,sosolvethe formula for r.
Divide both sides by t. S i m p l i f y .
π
Example
5
Hint
In the formula d = rt;
d is distance, r is rate or speed, and t is time.
d = rt d = rt
__
tt
_d = r t
Step2: Substitute270fordand4.5fort. _d = r
t
_2 7 0 = r
4.5
60 = r
The Ramirez family needs to average a speed of 60 mph to make the trip in
4_1 hours. 2
Lesson 29 173