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Question

If secθ+tanθ=p, prove that sinθ=p21p2+1

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Solution

R.H.S = p21p2+1

=(secθ+tanθ)21(secθ+tanθ)2+1

=sec2θ+tan2θ+2secθtanθ1sec2θ+tan2+2secθtanθ+1

[By (a+b)2=a2+b2+2ab]

=(sec2θ1)+tan2θ+2secθtanθsec2θ+(1+tan2θ)+2secθtanθ

=tan2θ+tan2θ+2secθtanθsec2θ+sec2θ+2secθtanθ

[sec2θ1=tan2θsec2θ=1+tan2θ]

=2tan2θ+2secθtanθ2sec2θ+2secθtanθ

=2tanθ(tanθ+secθ)2secθ(secθ+tanθ)=tanθsecθ

=sinθcosθ1cosθ

=sinθ = L.H.S

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