Question:
why cos(180-x)= - cos x
Answer:
We know that
cos(x-y) = cosx*cosy + sinx*siny
Now
cos(180-x) = cos180*cosx + sin180*sinx
= -1*cosx + 0*sinx (since cos180 = -1 and sin180 = 0)
= -cosx
So cos(180-x) = -cosx
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