Question

Evaluate the following :

Cos 28° - sin 42° =

Answer 1

cos 28° - sin 42°

= cos 28° - sin(90° - 28°)

= cos 28° - cos 28°

= 0

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Answer 2

Answer:

Step-by-step explanation:

Note: I think you have copied the question wrong because had the question been Cos48° - Sin42°, then the answer is 0.

But using the question given , the procedure to solve is as below:

Cos 28 = Cos (90 - 62) = Sin62 (∵ Cos (90-θ) = SInθ)

So Cos 28° - sin 42°

= Sin 62 - Sin 42  (∵ SinA - SinB = 2 Cos(A+B/2)Sin(A-B/2))

= 2 Cos (62+42/2)Sin (62-42/2)

= 2Cos52Sin10.

The only way to solve above is using trigonometric tables from here on .