caimengzhe
幼苗
共回答了17个问题采纳率:82.4% 举报
由韦达定理得X1+X2=-2,X1*X2=-3/2,
绝对值X1-X2
=根号[(X1-X2)²]
=根号[(X1+X2)²-4X1*X2]
=根号(4+6)
=根号10
1年前
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这一步[(X1+X2)²-4X1*X2]的4x1x2是什么意思?
举报
caimengzhe
(X1-X2)² =X1²-2X1*X2+X2² =X1²+2X1*X2+X2²42X1X2 =(X1+X2)²-4X1*X2
举报
caimengzhe
(X1-X2)² =(X1)²-2(X1)*(X2)+(X2)² =(X1)²+2(X1)*(X2)+(X2)²-4*(X1)*(X2) =(X1+X2)²-4X1*X2 (前三项完全平方)