Factor the expression

Question

-8x^2+22x-15

answer choices

a (2x+3)(5-4x)

B (2x-3)(5-4x)

c(4x+5)(2x-3)

d(3-2x)(5-4x)

Answer 1

-8x^2 + 22x - 15

You are going to need to find two numbers whose product is -8 * -15 = 120

and whose sum is 22.

Those two number are 10 and 12.

split 22x up into sum of 12x and 10x:

-8x^2 + 12x + 10x - 15

factor adjacent terms:

-4x (2x - 3) + 5(2x - 3)

distribute

(-4x + 5)(2x - 3)

which is the same as b)

Answer 2

Multiply out the solutions and compare or treat the solutions as zeros and plug into the equation to see if it's a zero.

For example a) has zeroes of -3/2 and 5/4

or you could skim through the solutions and check the constant and square terms

square term of -8 eliminates (C)

Constant term of -15 eliminates (A) and (D)