1.
3x^2+4x-7=0
3(x^2+2X2/3x+(2/3)^2)-4/3-7=0
3(x+2/3)^2=25/3
(x+2/3)^2=25/9
x+2/3=±5/3
x=±5/3-2/3
x=1或x=-7/3
2.
2x^2-8x+1=0
2(x^2-4x+4)-8+1=0
2(x-2)^2=7
(x-2)^2=7/2
x-2=±根号14/2
x=2±根号14/2
3.
（x-1）²-4（x-1)-21=0
(x-1)^2-2X2(X-1)+2^2-21-4=0
(X-1-2)^2=25
X-3=±5
x=8或x=-2
4.
3x²-1=4x
3x^2-4x-1=0
3(x^2-2X2/3x+(2/3)^2)-1-4/3=0
3(x-2/3)^2=7/3
(x-2/3)^2=7/9
x-2/3=±根号7/3
x=±根号7/3+2/3
5.
（2x+1）²=3（2x+1）
(2x+1)^2-3(2x+1)=0
(2x+1)(2x+1-3)=0
2(2x+1)(x-1)=0
即2x+1=0或x-1=0
x=-1/2或x=1
6.
x^2-7x+10=0
(x-5)(x-2)=0
x-5=0或x-2=0
x=5或x=2
7.
399=
x^2-2x-399=0
(x^2-2x+1)-1-399=0
(x-1)^2=400
x-1=±20
x=-19或x=21