1:y=2x²-3x+1
=2(x²-3x/2)+1
=2（x²-3x/2+9/16-9/16）+1
=2(x-3/4)²-9/8+1
=2(x-3/4)²-1/8
2：y=x²+5x
=x²+sx+25/4-25/4
=(x+5/2)²-25/4
3：y=x²+2x-4
=x²+2x+1-1-4
=(x+1)²-5
4: y=x²/2-7x-2
=1/2(x²-14x)-2
=1/2(x²-14x+49-49)-2
=1/2(x-7)²-49/2-2
=1/2(x-7)²-53/2
利用配方法解方程!求助题 y=2x²-3x+1