Respuesta :
The attached figure represents the cardboard (10inches by 12 inches) and the squares that should be cut to make the box.
let the length of the square = x
So , the length of the box = L = 12 - 2x
      the width of the box = W = 10 - 2x
And, the area = L * W = 80          ⇒(given)
∴  L * W = (12-2x)(10-2x) = 80
∴ (12 - 2x)(10-2x) =80              Â
   4x² - 44x + 120 = 80       ⇒ multiply the brackets    Â
   4x² - 44x +120 - 80 = 0   ⇒ make all variables in one side
   4x² - 44x + 40 = 0           ⇒ sum the similar
   x² - 11x +10 = 0              ⇒ solve by analysis
   (x-1)(x-10) = 0
∴    x = 10 (rejected because the cardboard length = 10 inch)
ORÂ x = 1
 ∴  the size of the square should be cut from each corner = 1 inch by 1 inch
let the length of the square = x
So , the length of the box = L = 12 - 2x
      the width of the box = W = 10 - 2x
And, the area = L * W = 80          ⇒(given)
∴  L * W = (12-2x)(10-2x) = 80
∴ (12 - 2x)(10-2x) =80              Â
   4x² - 44x + 120 = 80       ⇒ multiply the brackets    Â
   4x² - 44x +120 - 80 = 0   ⇒ make all variables in one side
   4x² - 44x + 40 = 0           ⇒ sum the similar
   x² - 11x +10 = 0              ⇒ solve by analysis
   (x-1)(x-10) = 0
∴    x = 10 (rejected because the cardboard length = 10 inch)
ORÂ x = 1
 ∴  the size of the square should be cut from each corner = 1 inch by 1 inch