（x-5)^2=2(x-5) x^2-10x+25=2x-10 x^2-10x-2x=-10-25 x^2-12x=-35 x^2-2*6*x+6^2=-35+6^2 (x-6)^2=-35+36 (x-6^2)=1 x-6=正负1 x-6=1或x-6=-1 x1=7或x2=5