Evaluate : 2(tan 35° / cot 55°)^2 + (cot 55° / tan 35°) - 3(sec 40° / cosec 50°)

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If 2 sin A - 1 = 0, show that :
sin 3A = 3 sin A - 4 sin³ A

If 4 cos² A - 3 = 0, show that :
cos 3A = 4 cos³ A - 3 cos A