Answer :

Given:




We know,


sin2 x + cos2 x = 1


cos2 x = 1 – sin2 x








Since,



cosx will be negative in second quadrant


So,



We know,


cos 2x = 2 cos2 x – 1









Since,




So,



We know,


cos 2x = 1 – 2 sin2 x









Since,




So,



We know,





On rationalising:




{ (a + b)(a – b) = a2 – b2}






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