(5x-7)(8x+1)=(8x+1)²

40x²-56x+5x-7=64x²+16x+1

40x²-51x-7=64x²+16x+1

40x²-51x-7-64x²-16x-1=0

-24x²-67x-8=0

24x²+67x+8=0

24x²+64x+3x+8=0

8x(3x+8)+3x+8=0

(3x+8)(8x+1)=0

x1=-8/3, x2=-1/8

x1=-2 2/8, x2=-1/8