麻烦各位帮我解个一元二次方程吧5x(x-3)=21-7x2x^2-5x+1=03x^2+7x+2=0

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麻烦各位帮我解个一元二次方程吧5x(x-3)=21-7x2x^2-5x+1=03x^2+7x+2=0
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麻烦各位帮我解个一元二次方程吧5x(x-3)=21-7x2x^2-5x+1=03x^2+7x+2=0
麻烦各位帮我解个一元二次方程吧
5x(x-3)=21-7x
2x^2-5x+1=0
3x^2+7x+2=0

麻烦各位帮我解个一元二次方程吧5x(x-3)=21-7x2x^2-5x+1=03x^2+7x+2=0
(1) 5x(x-3)=21-7x
=>5x^2-8x-21=0
=>(x+3)(5x-7)=0
=>x=-3 or x=7/5
2x^2-3x+1=0
=>(x-1)(2x-1)=0
=>x=1 or x=1/2
3x^2+7x+2=0
=>(x+2)(3x+1)=0
=>x=-2 or x=-1/3

由题目所得:
5X^2-8X-21=0所以(X-0.8)^2=4.84
X=3或X=-7/5
由3x^2+7x+2=0得出(X+7/6)^2=25/36
所以X=-1/3或X=-2
2x^2-5x+1=0得出(X-5/4)^2=17/16
所以X=5/4±√17/8