Q16 of 48 Page 84

Prove the following with the help of identities:

sin6θ + cos6θ = 1 – 3sin3θ cos2θ

Using the identity: a3 + b3 = (a + b)(a2 + b2 – ab)


Here, a = sin2 θ and b = cos2 θ


(sin2 θ + cos2 θ)(sin4 θ + cos4 θ – sin2 θ.cos2 θ)


Now, Using: sin2θ + cos2θ = 1 and a2 + b2 = (a + b)2 – 2.a.b


(1)((sin2 θ + cos2 θ)2 – 2.sin2 θ.cos2 θ – sin2θ.cos2θ )


((1)2 – 2.sin2 θ.cos2 θ – sin2 θ.cos2 θ)


(1 – 3.sin2 θ.cos2 θ)


= R.H.S


Hence, proved.


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