已知(a²+2b²)(a²+2b²-1)=12,求5a²+10b²的值
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已知(a²+2b²)(a²+2b²-1)=12,求5a²+10b²的值
已知(a²+2b²)(a²+2b²-1)=12,求5a²+10b²的值
已知(a²+2b²)(a²+2b²-1)=12,求5a²+10b²的值
(a²+2b²)(a²+2b²-1)=12
(a²+2b²)²-(a²+2b²)=12
(a²+2b²)²-(a²+2b²)-12=0
解得a²+2b²=4或-3,因a²+2b²≥0,所以只取a²+2b²=4
5a²+10b²=5(a²+2b²)=5×4=20
(a²+2b²)(a²+2b²-1)=12
(a²+2b²)² -(a²+2b²) -12 =0
(a²+2b² -4)(a²+2b² +3)=0
a²+2b² =4 a²+2b²=-3 (舍掉)
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(a²+2b²)(a²+2b²-1)=12
(a²+2b²)² -(a²+2b²) -12 =0
(a²+2b² -4)(a²+2b² +3)=0
a²+2b² =4 a²+2b²=-3 (舍掉)
5a²+10b²
=5(a²+2b²)
=5×4 =20
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令x=a²+2b²
则x(x-1)=12
x²-x-12=0
(x+3)(x-4)=0
x=-3,x=4
因为x=a²+2b²≥0
所以a²+2b²=4
所以原式=5(a²+2b²)=20