(7x+1)(x-3)+20 (x-1)(x+1)=3 (3x-2)²+13
7x²-21x+x-3+20(x²-1)=3(9x²-12x+4)+13
7x²-21x+x-3+20x²-20=27x²-36x+12+13
7x²-21x+x-3+20x²-20-27x²+36x-12-13=0
14x-28=0
14x=28
x=2
(7x+1)(x-3)+20 (x-1)(x+1)=3 (3x-2)²+13
7x²-21x+x-3+20(x²-1)=3(9x²-12x+4)+13
7x²-21x+x-3+20x²-20=27x²-36x+12+13
7x²-21x+x-3+20x²-20-27x²+36x-12-13=0
14x-28=0
14x=28
x=2