SOLUTION: Proof the identity What happens if you get Cos (A-360).

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Question 1019407: Proof the identity
What happens if you get Cos (A-360).
Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
cosine (a - 360) should be equal to cosine (a).

this is because the graph of cosine (a) will repeat every 360 degrees.

here's what the graph looks like.

$$$

the graph is of the equation y = cos(x).

there are 2 vertical lines.

one is at x = 30 and one is at x = 30 - 360.

30 - 360 is equal to - 330 as sh own on the graph.

you can see that the cosine function is the same for both angles.

using the trigonometric identity function of cos(a-b) should get you the same result when you assume that b is equal to 360 degrees.

the identity function is:

sin(a - b) = sin(a)cos(b) – cos(a)sin(b)

when b = 360 degrees, then

sin(360) = 0
cos(360) = 1

the formula of sin(a - b) = sin(a)cos(b) – cos(a)sin(b) becomes:

sin(a - 360) = sin(a)cos(360) - cos(a)sin(360) which becomes:

sin(a - 360) = sin(a)*1 - cos(a)*0 which becomes:

sin(a - 360) = sin(a)