求证(1-sinθcosθ)除以(cos^2θ-sin^2θ)=(cos^2θ-sin^2θ)除以(1+2sinθcosθ)

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求证(1-sinθcosθ)除以(cos^2θ-sin^2θ)=(cos^2θ-sin^2θ)除以(1+2sinθcosθ)
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求证(1-sinθcosθ)除以(cos^2θ-sin^2θ)=(cos^2θ-sin^2θ)除以(1+2sinθcosθ)
求证(1-sinθcosθ)除以(cos^2θ-sin^2θ)=(cos^2θ-sin^2θ)除以(1+2sinθcosθ)

求证(1-sinθcosθ)除以(cos^2θ-sin^2θ)=(cos^2θ-sin^2θ)除以(1+2sinθcosθ)
是 (1 -2 sin θ cos θ) /[ (cos θ)^2 -(sin θ)^2 ] = [ (cos θ)^2 -(sin θ)^2 ] / (1 +2 sin θ cos θ)
= = = = = = = = =
证明:因为 (cos θ)^2 -(sin θ)^2 =(cos θ +sin θ) (cos θ -sin θ),
1 -2 sin θ cos θ =(sin θ)^2 +(cos θ)^2 -2 sin θ cos θ
=(cos θ -sin θ)^2,
同理,1 +2 sin θ cos θ =(cos θ +sin θ)^2,
所以 左边 =(cos θ -sin θ) /(cos θ +sin θ),
右边 =(cos θ -sin θ) /(cos θ +sin θ).
所以 左边 =右边.
= = = = = = = = =
常用变换:
1 +2 sin θ cos θ =(cos θ +sin θ)^2,
1 -2 sin θ cos θ =(cos θ -sin θ)^2.