Question 403986
A wire 310 in. long is cut into two pieces. One piece is formed into a square and the other into a circle.
If the two figures have the same area, what are the lengths of the two pieces of wire (to the nearest tenth of an inch)?
:
Let s = the side of the square
then
4s = the perimeter of the square
s^2 = the area of the square
:
Let r = the radius of the circle
then
{{{2*pi*r}}} = the circumference of the circle
{{{pi*r^2}}} = area of the circle
:
"the two figures have the same area,
s^2 = {{{pi*r^2}}}
s = {{{sqrt(pi*r^2)}}}

:
"A wire 310 in. long is cut into two pieces."
:
Perimeter + Circumference = 310 inches
4s + {{{2*pi*r}}} = 310
:
Replace s with {{{sqrt(pi*r^2)}}}
{{{4(sqrt(pi*r^2)) + (2*pi*r)}}} = 310
:
simplify, divide by 2, Extract r
{{{2r(sqrt(pi)) + (pi*r)}}} = 155
:
Change pi to decimal values
2r(1.772) + r(3.1416) = 155
3.545r + 3.1416r = 155
6.6865r = 155
r = {{{155/6.6865}}}
r = 23.18
:
Find the circumference
C = {{{2*pi*23.18}}}
C = 145.7 inches the length of the wire to make the circle
then
310 - 145.7 = 164.3 inches is the length to make the square
:
:
Check this by finding the area of circle and the square
Square: (164.3/4)^2 = 1687.155 sq/inches
Circle: {{{pi*23.18^2}}} = 1688.0 sq/inches, discrepancy is from rounding off