(a+2b)^2=7,(a-2b)^2=3,求a^2+4b^2的值和ab的值
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![(a+2b)^2=7,(a-2b)^2=3,求a^2+4b^2的值和ab的值](/uploads/image/z/1816955-35-5.jpg?t=%28a%2B2b%29%5E2%3D7%2C%28a-2b%29%5E2%3D3%2C%E6%B1%82a%5E2%2B4b%5E2%E7%9A%84%E5%80%BC%E5%92%8Cab%E7%9A%84%E5%80%BC)
(a+2b)^2=7,(a-2b)^2=3,求a^2+4b^2的值和ab的值
(a+2b)^2=7,(a-2b)^2=3,求a^2+4b^2的值和ab的值
(a+2b)^2=7,(a-2b)^2=3,求a^2+4b^2的值和ab的值
(a+2b)^2=7,(a-2b)^2=3两式展开相加得,a²+4b²=5,
2ab=(a+2b)²-(x²+4y²)=7-5=2,所以ab=1
分别将两式左右两边相加和相减,自己试试看~~
a+2b=根号7
a-2b=根号3
两式相加得2a=根号7+根号3
两式相减得4b=根号7-根号3
直接代入后式计算就可以了