1.

Prove that cot x cot2x – cot2x cot3x – cot3x cotx = 1.

Answer»

Consider cot 3x = cot(2x + x)

= (cos2xcotx - 1)/(cot2x + cotx)

⇒ cot 3x(cot 2x+cot x) – cot 2x cot x -1 

⇒ 1 = cot 2x cot x – cot 3x cot 2x – cot 3x cot x



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