求证 (1/sin^2 x) + (1/cos^2 x) - (1/tan^2 x)= 2 + (tan^2 x)
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求证 (1/sin^2 x) + (1/cos^2 x) - (1/tan^2 x)= 2 + (tan^2 x)
怎么证明啊……?
怎么证明啊……?
(1/sin^2 x) + (1/cos^2 x) - (1/tan^2 x)= (1/sin^2 x*cos^2 x)-(cos^2 x/sin^2 x)
=(1-cos^4x)/sin^2 x*cos^2 x
=(1+cos^2x)sin^2x/sin^2 x*cos^2 x
==(1+cos^2x)/cos^2 x
=sec^2x+1=1+tan^2x+1= 2 + (tan^2 x)
=(1-cos^4x)/sin^2 x*cos^2 x
=(1+cos^2x)sin^2x/sin^2 x*cos^2 x
==(1+cos^2x)/cos^2 x
=sec^2x+1=1+tan^2x+1= 2 + (tan^2 x)
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