a-b=9 ab=5 求a²+b²,(a+b)²的值a-b=9 ab=5 求a²+b²,(a+b)²的值.
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a-b=9 ab=5 求a²+b²,(a+b)²的值a-b=9 ab=5 求a²+b²,(a+b)²的值.
a-b=9 ab=5 求a²+b²,(a+b)²的值
a-b=9 ab=5 求a²+b²,(a+b)²的值.
a-b=9 ab=5 求a²+b²,(a+b)²的值a-b=9 ab=5 求a²+b²,(a+b)²的值.
a-b=9
两边平方
a²-2ab+b²=81
所以
a²+b²
=81+2ab
=81+10
=91
(a+b)²
=a²+2ab+b²
=91+10
=101
∵a-b=9
∴(a-b)²=81
a²-2ab+b²=81
∵ab=5
∴a²-2×5+b²=81
∴a²+b²=91
∴a²+2ab+b²=101
∴(a+b)²=101
(a-b)^2=81=a^2+b^2-2ab;
=> a^2+b^2=91
(a+b)²=a^2+b^2+2ab=101
(a-b)^2=a^2-2ab+b^2=81
a^2+b^2=81+10=91
(a+b)^2=a^2+2ab+b^2=91+10=101