Question

Find an integer value of b that makes x^2 + bx - 81 factorable.

Answer 1

b = 80

Explanation:

Given that,

x² + bx - 81

To find,

value of b

What is factorable?

A polynomial equation with highest degree 2 is if factorable when

1. we can find two terms which when multiples = -81x², ( x² * - 81 = -81x² )
2. and when add = bx

possible factors:

1. -1x * 81x = -81x² (Accepted)
2. 1x * -81x= -81x² (rejected)
3. 9x * -9x = -81x² (rejected)
4. -9x * 9x = -81x² (rejected)

Only when -1x , 81x is added -1x + 81x = 80x

so, bx = 80x

b = 80

The equation is x² + 80x - 81