Question

The area of a rectangle can be expressed by 2x2 – 7x – 4. If the rectangle has an

area of 45, find the positive value for x.

Answer 1

7

Explanation:

2x^2 - 7x - 4 = 45

2x^2 - 7x - 49 = 0 : subtract 45 from both sides

Quadratic formula:

x = (7 ± sqrt(7^2 - 4*2*-49) ) / 4

x = (7 ± sqrt(49 - -392)) / 4

x = (7 ± sqrt(441)) / 4

x = (7 ± 21) / 4

x = (7 + 21) / 4 OR x = (7 - 21) / 4

x = 28 / 4 OR x = -14 / 4

x = 7 as it is the only positive answer