8x+mx2−3x−4≡5x+1+3x−4
8x+mx2−3x−4 ≡ 5(x−1)+3(x+4)x2−3x−4
multiplying both sides by x2-3x-48x+m ≡ 5(x-4)+3(x+1)8x + m ≡ 5x - 20 + 3x + 38x - 5x - 3x + m = -20 + 3m = -17