x²+2x+1=4
(x+1)²=4
x+1=2或x+1=-2
解得x=1或x=-3
x²-x-3/4=0
x²-x+1/4=1
(x-1/2)²=1
x-1/2=1或x-1/2=-1
解得x=3/2或x=-1/2
4x²-x-9=0
4x²-x+1/16=9+1/16
(2x-1/4)²=145/16
2x-1/4=√145 /4或2x-1/4=-√145 /4
解得x=(√145+1)/8或x=(1-√145)/8
　　祝学习快乐