Question 199290
Let x be the length of the square piece of cardboard.
(x-4*2)^2 this accounts for the two 4 in. corners cut out.
(x-8)^2 is the bottom area.
4 inches is the height.
4(x-8)^2=100
4(x^2-16x+64)=100
4x^2-64x+256-100=0
4x^2-64x+156=0
4(x^2-16+39)=0
(x-13)(x-3)=0
x-13=0
x=13 ans. for the original length of the square piece of cardboard.
Proof:
(13-8)^2=5^2=25
4*25=100
100=100