Question

A square piece of paper has an area of x2 square units. A rectangular strip with a width of 2 units and a length of x units is cut off of the square piece of paper. The remaining piece of paper has an area of 120 square units.

Which equation can be used to solve for x, the side length of the original square?

x2 − 2x − 120 = 0
x2 + 2x − 120 = 0
x2 − 2x + 120 = 0
x2 + 2x + 120 = 0

Answer 1

Original area = x^2. Removed area = 2 · x = 2x. Remaining area: x^2 − 2x = 120. Rearranged gives x^2 − 2x − 120 = 0.

So the correct equation is: x^2 − 2x − 120 = 0.