SOLUTION: show that cos75°-cos15°= -1/√2

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Question 1109057: show that cos75°-cos15°= -1/√2
Answer by abdulaleem(11) About Me  (Show Source):
You can put this solution on YOUR website!
Cos75°- Cos15°
From the formula
CosA- CosB= -2Sin(A+B/2)Sin(A-B/2)
Cos75°- Cos15°= -2Sin(75°+15°/2)Sin(75°-15°/2)
= -2Sin45°Sin30°
As Sin45°= 1/√2 and Sin30°= 1/2
So = -2(1/√2)(1/2)
= -1/√2