已知a-b=7,ab=2,求a²+b²和(a+b)²的值.
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已知a-b=7,ab=2,求a²+b²和(a+b)²的值.
已知a-b=7,ab=2,求a²+b²和(a+b)²的值.
已知a-b=7,ab=2,求a²+b²和(a+b)²的值.
53
57
a²+b²=(a-b)²+2ab=7²+2×2=49+4=53
(a+b)²=(a-b)²+4ab=7²+4×2=49+8=57
可以先将a-b=7两边同时平方就得
a²-2ab+b²=49,又因为ab=2
所以a²+b²=53
(a+b)²=a²+2ab+b²=53+4=57