Q22 of 48 Page 84

Prove the following with the help of identities:

sin8θ – cos8θ = (sin2θ – cos2θ) (1– 2sin2θ cos2θ)

Taking L.H.S we get,


Sin8 θ– cos8 θ


Using the formula: a2 – b2 = (a – b)(a + b)


(sin4 θ – cos4 θ)(sin4 θ + cos4 θ)


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


(sin2 θ – cos2 θ)(1)((1)2 – 2.sin2 θ.cos2 θ) (Using: sin2 θ + cos2 θ = 1.)


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


= R.H.S


Hence, proved


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