a^2-5a-2=0,
a²-5a+25/4=33/4
(a-5/2)²=33/4
∴a=5/2±√33/2
x^2-3/4x=0,
x²-3x/4+9/64=9/64
(x-3/8)²=9/64
x-3/8=3/8 x-3/8=-3/8
x=3/4 x=0
5x^2-15x+11=0,
x²-3x=-11/5
x²-3x+9/4=1/20
(x-3/2)²=5/100
∴x=3/2±√5/10
2x^2-4倍根号下3x+5=0,
x²-2√3x=-5/2
x²-2√3x+3=1/2
(x-√3)²=2/4
∴ x=√3±√2/2
3/4x^2-x-1/2=0
x²-4/3x+4/9=10/9
(x-2/3)²=10/9
∴x=2/3±√10/3
先做到这儿吧