Q5 of 268 Page 4

Prove the following :

cos90° = 1 – 2 sin245° = 2cos245° – 1

We know that


cos(90o) = 0




taking LHS = cos 90° = 0


Now solving RHS 1- 2sin2 45°




= 1- 1


= 0


= RHS


Now, solving RHS = 2cos2 45° - 1 , we get




= 1- 1


= 0


Hence, proved.


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