Q. 375.0( 1 Vote )

Prove that: .

Answer :

Formula : -


(i) Cos 3 a = 4 cos3 a – 3 cos a


(ii) sin3a = 3sina – 4sin3a


(iii) a3 – b3 = (a2 – b2)(a2 + b2 + ab)


(iv) sin2a + cos2a = 1


Taking L.H.S we get,



using formula (i) and (ii)



taking common (cos a – sin a) and using formula (iii)



using formula(iv)




L.H.S = R.H.S


Hence, Proved.


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