已知tan^2a=2tan^2b+1,求证:sin^b=2sin^2a-1

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已知tan^2a=2tan^2b+1,求证:sin^b=2sin^2a-1
已知tan^2a=2tan^2b+1,求证:sin^b=2sin^2a-1

已知tan^2a=2tan^2b+1,求证:sin^b=2sin^2a-1
tan^2a=2tan^2b+1
sin^2a/cos^2a=2*sin^2b/cos^2b+2-1
sin^2a/cos^2a+1=2*sin^2b/cos^2b+2
1/cos^2a=2/cos^2b
cos^2b=2*cos^2a
所以
1-sin^2b = 2(1-sin^2)=2-2sin^2a
整理得
sin^b=2sin^2a-1

化切为弦,使用倍角公式……