## Thinking Mathematically (6th Edition)

$12x^{2}$ - x -20 = (4x+5) (3x__) step 1. Find two first terms whose product is $12x^{2}$ $12x^{2}$ - x -20 = (4x+5) (3x__) which is given and Step 2. To find the second term of each factor, we must find two integers whose product is -20 and whose sum is -1 List pairs of factors of the constant, -20 (1,-20)(-1,20)(-4,5)(4,-5)(2,-10)(-2,10) step 3. The correct factorization of $12x^{2}$ - x -20 is the one in which the sum of the Outside and Inside products is equal to -x. list of the possible factorization : (4x+5)(3x-4) = $12x^{2}$ - x -20 (4x-5)(3x+4) = $12x^{2}$ + x -20 So, (4x+5)(3x-4) is the solution