# TRIG-Straight line implied that sum of the two angles for the cosines equal 0. WHY?Watch

#1
"a straight line implied that sum of the two angles for the cosines equal 0"

I don't understand how it = 0, thing is i thought that cos(180) = -1 so how did cos(180) = 0 shouldn't it be sin(180) = 0

Is there a rule that I'm unaware of, where cosine magically becomes sine.
Can someone please explain how this works
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4 years ago
#2
(Original post by Ysky)
"a straight line implied that sum of the two angles for the cosines equal 0"

I don't understand how it = 0, thing is i thought that cos(180) = -1 so how did cos(180) = 0 shouldn't it be sin(180) = 0

Is there a rule that I'm unaware of, where cosine magically becomes sine.
Can someone please explain how this works
Cosine for right angles is 0, never heard that one before

There is, sin(x)=cos(90-x).

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