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春芽
共回答了21个问题采纳率:85.7% 举报
ax^2+bx+c=0
a(x^2+bx/a)=-c
a(x^2+bx/a+b^2/4a^2)=b^2/4a-c
a(x+b/2a)^2=(b^2-4ac)/4a
(x+b/2a)^2=(b^2-4ac)/4a^2
x+b/2a=±√(b^2-4ac)/2a
x=[-b±√(b^2-4ac)]/2a
x1=[-b+√(b^2-4ac)]/2a,x2=[-b-√(b^2-4ac)]/2a
x1+x2=[-b+√(b^2-4ac)]/2a +[-b-√(b^2-4ac)]/2a
=-2b/2a=-b/a
x1*x2=[-b+√(b^2-4ac)]/2a *[-b-√(b^2-4ac)]/2a
= [b^2-(b^2-4ac)]/4a^2
=(b^2-b^2+4ac)/4a^2
=c/a
1年前
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