1.

Sin8A+Cot8A=1-4Sin2A.Cos2A+2Sin4A.Cos4A

Answer»

(sin2 A + cos2 A)2 = 12

sin4 A + 2sin2A cos2 A +cos4 A = 1

You need to isolate the sum sin4 A + cos4  A to the left side such that:

sin4 A + cos4 A = 1 - 2sin2A cos2 A

You need to raise to square both sides such that:

(sin4 A + cos4 A) = (1 - 2sin2A cos2 A)2

sin8 A + 2sin4 Acos4 A + cos8 A = 1 - 4sin2A cos2 A + 4sin4 A cos4 A

Moving to the right 2sin4 Acos4 A  yields:

sin8 A +cos8 A = 1 - 4sin2A cos2 A + 4sin4 A cos4 A - 2sin4 Acos4  A

sin8 A + cos8 A = 1 - 4sin2A cos2 A + 2sin4 A cos4 A



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