a+b=7 ab=1 求a^2+b^2 a^2-3ab+b^2
4个回答
a^2+b^2
=(a²+2ab+b²)-2ab
=(a+b)²-2ab
=7²-2
=47
a^2-3ab+b^2
=(a²+2ab+b²)-5ab
=(a+b)²-5ab
=7²-5
=44
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