Question

Find the exact value of the expression cos (-105)

Answer 1

cos(-©) negative angle is cos(+©) angle cos(-105) =cos(105) 105 =180-75 cos(180-75)= - cos(75) - cos(75)= - 0.26

Answer 2

cos(-105) = cos105 = cos(90+15) = cos90cos15 - sin90sin15 = 0.cos15 - 1.sin5 = 0 - sin15 = -sin15