Question

David wants to hang a mirror in his room. The mirror and frame must have an area of 8 square feet. The mirror is 2 feet wide and 3 feet long. Which quadratic equation can be used to determine the thickness of the frame, x?
Square with an inner frame with height of 2ft on the left frame and width of 3ft on the top. Arrow on the bottom frame with an x and an arrow on the right frame with an x.


2x2 + 14x − 2 = 0
3x2 + 10x − 8 = 0
4x2 + 10x − 2 = 0
x2 + 7x − 8 = 0

Answer 1

Represent the thickness of the frame by x. Framing the mirror will increase both its length and width by 2x. The area of the mirror with the frame is the product of the length and width which can mathematically be expressed as,
                                 
                                                A = (3 + 2x)(2 +2x) = 8

The equation above can be simplified into 4x^2 + 10x -2 = 0. This equation can still be further simplified by dividing it by 2. However, it will give an answer which is not found on the choices. Thus, the answer is the third choice.