(a+b)²=49,(a-b)²=9,求a²+b²,ab的值
问题描述：
(a+b)²=49,(a-b)²=9,求a²+b²,ab的值
答
(a+b)²+(a-b)²
=a^2+2ab+b^2+a^2-2ab+b^2
=2a^2+2b^2
=2(a^2+b^2)=58
a^2+b^2=29
(a+b)²-(a-b)²=a^2+2ab+b^2-a^2+2ab-b^2
=4ab=40
ab=10