解
2(x-1)=x-5
2x-2=x-5
2x-x=2-5
x=-3
3x²-(2x²-x+1)+2(x-x²-3)
=3x²-2x²+x-1+2x-2x²-6
=(3x²-2x²-2x²)+(x+2x)+(-6-1)
=-x²+3x-7
=-(-3)²+3×(-3)-7
=-9-9-7
=-25