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Prove that: (costheta)/(1+sintheta)=tan...

Prove that: `(costheta)/(1+sintheta)=tan(pi/4-theta/2)`

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`L.H.S. = cos theta/(1+sintheta)`
`= sin(pi/2-theta)/(1+cos(pi/2 - theta))`
Using `sin2x = 2sinxcosx and 1+cos2x = 2cos^2x`
`=(2sin(pi/4-theta/2)cos(pi/4-theta/2))/(2cos^2(pi/4-theta/2))`
`=sin(pi/4-theta/2)/cos(pi/4-theta/2)`
`=tan(pi/4-theta/2) = R.H.S`
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