已知(a-b)²=25 ab=-2 求a²+b²+ab和(a+b)²的值
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已知(a-b)²=25 ab=-2 求a²+b²+ab和(a+b)²的值
已知(a-b)²=25 ab=-2 求a²+b²+ab和(a+b)²的值
已知(a-b)²=25 ab=-2 求a²+b²+ab和(a+b)²的值
即a²-2ab+b²=25
a²+b²=25+2ab=21
所以a²+b²+ab
=21-2
=19
(a+b)²
=a²+2ab+b²
=21-4
=17
a²+b²+ab=a²-2ab+b²+3ab=(a-b)²+3ab=25+3*(-2)=19
(a+b)²=a²+2ab+b²=a²+b²+ab+ab=19+(-2)=17