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If A + B + C = 180°, prove that
Solution:
Consider the given equation above
In proving of trigonometric identities, we have to choose first the more complicated part and then simplify until it match with the other side of the equation. In this case, we have to choose the right side of the equation as follows
Use the Sum and Product Formula, we have
but
Therefore, the above equation becomes
Therefore, the identity is correct for