math
posted by nicole on .
by cutting a square out of each corner of a sheet of card (30cm by 21cm)and folding up the sides,i ca make an open box with a capacity of 1080cm^3.What is the area in cm^2 of each of the squares i have to cut out?

this problem has been solved in many of the related questions below, with different numbers. Follow some of them and give it a shot. What do you get?

Let the sides you cut out be x centimetres long.
The volume is then:
(302x)(212x)x = 1080
Expanding:
4 x^3  102 x^2 + 630 x  1080 = 0
Look for common factors:
(x3)(4x^2  90x + 360) = 0
Found one root, solve the quadratic for the other.