Question

Упростите выражение: cos105-cos75

Answer 1

cos105-cos75 = -2 sin (105+75)/2 * sin(105-75)/2= -2sin90 * sin 15=-2sin15

Answer 2

cos105-cos75=-2sin15sin90=-2sin15
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cosa-cosb=-2sin(a-b)/2*sin(a+b)/2