problem with finding the minimum area
A piece of wire of length 8cm is cut into two pieces,one of length x cm,the other of length (8-x)cm.The piece of lenght x cm is bent to form a circle with circumference x cm. The other piece is bent to form a square with perimeter (8-x)cm. Show that , as x varies, the sum of the areas enclosed by these two pieces of wire is a minimum when the radius of the circle is
i found the area of the square to be
and the the radius of the circle is so the area of circle is
i add them up and i differentiate the eqn. i got
At min point, =0
then when i sub it into the radius, i did not get the ans. what is wrong?