(x-7)²=4(1-x)²
(x-7)²=4(x-1)²
4(x-1)²-(x-7)²=0
[2(x-1)+(x-7)][2(x-1)-(x-7)]=0
(3x-9)(x+5)=0
3(x-3)(x+5)=0
x1=3,x2=-5