第1个回答 2012-10-10
1）x²－x－3/4=0 ,x²－x=3/4 ,(,x-1/2)²=3/4+1/4=1 , x1=3/2, x2=-1/2
(2) 3x²+6x－5=0 , x²+2x=5/3 , (x+1)²=8/3 , x1=-1-2√6/3 ,x2=-1-+2√6/3
(3)4x²－x－9=0 , x²-x/4=9/4 , (x-1/8)²=9/4+1/64 , x1=(1-√145)/8 ,x2=(1+√145)/8本回答被提问者采纳
第2个回答 2012-10-10
x²-x-3/4=0
x²-x=3/4
x²-x+(1/2)²=3/4+(1/2)²
(x-1/2)²=1
x-1/2=±1
x1=-1/2 x2=3/2
(2) 3x²+6x－5=0
3(x²+2x-5/3)=0
x²+2x-5/3=0
x²+2x=5/3
x²+2x+1=5/3+1
(x+1)²=8/3
x+1=±(2/3)∨6
x1=-(2/3)√6-1 x2=(2/3)√6-1
(3)4x²－x－9=0
4(x²-1/4x-9/4)=0
x²-1/4x-9/4=0
x²-1/4x=9/4
x²-1/4x+(1/8)²=9/4+1/64
(x-1/8)²=145/64
x-1/8=±√145/8
x1=-√145/8+1/8 x2=√145/8