# Trigonometry

Write cos(-83degrees) as a function of a positive angle

Prove that tan^2(alpha)-1+cos^2(alpha)=tan^2(alpha)sin^2(alpha)

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1. since cos(-x) = cos(x), what do you think?

cos(-x) = cos(0-x)
= cos0*cosx - sin0*sinx
= 1*cosx - 0
= cos(x)

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