Question

cos10° cos30° cos50° cos70° = 3\16

Answer 1

cos10.cos30.cos50.cos70 = 3/16

L.H.S. = cos30.cos10.cos50.cos70

  = root(3)/2 × cos10.cos50.cos70

  = root(3)/4 × (cos60 + cos40)cos70

  = root(3)/8 × 2cos60.cos70 + 2cos40.cos70

  = root(3)/8 × (cos70 + cos110 + cos30)

  = root(3)/8 × (cos70 - cos70 + root(3)/2)

  = [root(3) × root(3)] / (8×2)

  = 3/16 = R.H.S.

Hence, proved.

Answer 2

Step-by-step explanation:

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