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Question -

sinx + cosx= 1 – 3 sinx cosx



Answer -

Let us consider LHS: sinx+ cosx

(sinx) 3 +(cosx) 3

By using the formula, a3 + b3 =(a + b) (a2 + b2 – ab)

(sinx + cosx)[(sinx) 2 +(cosx) 2 –sinx cosx]

By using the formula, sinx + cosx= 1 and a2 + b2 = (a + b) 2 –2ab

1 × [(sinx + cosx) 2 – 2sinxcosx – sinx cosx

12 –3sinx cosx

1 – 3sinx cosx

= RHS

LHS = RHS

Hence proved.

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