Question

cos30-cos50+cos70-co90=4sin10cos20sin60

Answer 1

Given, cos30 * cos10 * cos50 * cos70

= √3/2 * cos10 * cos50 * cos70

= √3/4 * (cos60 + cos40)cos70

= √3/8 * 2cos60 * cos70 + 2cos40 * cos70

= √3/8 * (cos70 + cos110 + cos30)

= √3/8 * (cos70 - cos70 + √3/2)

= (√3 * √3)/ (8 * 2)

= 3/16

Hence, cos30 * cos10 * cos50 * cos70 = 3/16