How do you find the perimeter or circumference, and the area of a circle with radius 4.2 in?

1 Answer
Jun 13, 2018

Answer:

See a solution process below:

Explanation:

The formula for the perimeter or circumference of a circle is:

#C= 2pir#

The formula for the area of a circle is:

#A_c = pir^2#

In both formulas #r# represents the radius of the circle.

Substituting #4.2" in"# for #r# in both formulas gives:

Circumference:

#C= 2pir# becomes:

#C= 2pi * 4.2" in"#

#C= 8.4pi" in"#

If you need a number we can substitute #3.14# for #pi# giving:

#C = 8.4 * 3.14" in" = 26.376" in"#

Area:

#A_c = pir^2# becomes:

#A_c = pi * (4.2" in")^2#

#A_c = 17.64pi" in"^2#

Again, if you need a number we can substitute #3.14# for #pi# giving:

#A_c = 17.64 * 3.14" in"^2 = 55.3896" in"^2#