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如题所述

1 x^2-3x+1=0
x^2-3x+9/4-9/4+1=0
(x-3/2)^2=5/4
x-3/2=根号5/2 x-3/2=-根号5/2
x=根号5/2+3/2 x=-根号5/2+3/2

2 2x^2+6=7x
x^2-7/2x+3=0
x^2-7/2x+49/16-49/16+3=0
(x-7/4)^2=1/16
x-7/4=1/4 x-7/4=-1/4
x=2 x=3/2

3 3x^2-9x+2=0
x^2-3x+2/3=0
x^2-3x+9/4-9/4+2/3=0
(x-3/2)^2=19/12

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第1个回答  2013-09-06
(1)解:x^2-3x+9/4-9/4+1=0
(x-3/2)^2=5/4
x-3/2=±√(5/4)
x=(3±√5)/2
(2)解:x^2-7/2x+3=0
x^2-7/2x+49/16-49/16+3=0
(x-7/4)^2=1/16
x-7/4=±√(1/16)
x=7/4±1/4
(3)解:x^2-3x+2/3=0
x^2-3x+9/4-9/4+2/3=0
(x-3/2)^2=19/12
x-3/2=±√(19/12)
x=(9±√57)/6
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