已知,a-b=6,ab=5,求a²-b²=
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已知,a-b=6,ab=5,求a²-b²=
已知,a-b=6,ab=5,求a²-b²=
已知,a-b=6,ab=5,求a²-b²=
a-b=6,ab=5
(a+b)²=a²+2ab+b²
=a²-2ab+b²+4ab
=(a-b)²+4ab
=6²+4×5
=36+20
=56
即
a+b=±√56=±2√14
所以
a²-b²=(a-b)(a+b)=6×(±2√14)=±12√14