Verify the identity using one side

Calculus
Tutor: None Selected Time limit: 1 Day

(cot(theta) - 1)/(cot(theta) + 1) = (1 - sin2(theta))/(cos2(theta))

Mar 20th, 2015

Dear friend please take theta = x ( it is easy in solving )

Cot x - 1 / cotx + 1

( cos x /sinx - 1 ) /( cosx/sinx + 1 )

(cosx - sinx) / sinx / (cosx + sinx ) / sinx

Cancelling sinx from numerator and denominatior

(cosx - sinx) /( cosx + sinx)

multiply numberatior and denominator by cosx - sinx

(cosx - sinx )(cosx - sinx) / (cosx + sinx ) ( cosx - sinx )

(cosx - sinx )^2/cos^2x - sin^x

cos^2x + sin^2x - 2sinx cosx / cos2x

cos^2x - sin^2x = cos2x ( identitiy used )

1 - sin2x / cos2x 

cos^2x + sin^2 x = 1

2 sinx cosx = sin2x

1 - sin2x / cos2x 

Now you may replace x by theta

1 - sin2theta / cos2theta

Hence Proved.


Mar 20th, 2015

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