Discussion

In \(\triangle ABC\), the side BC is extended to D. If \(\angle ACD = 120°\) and \(\angle ABC = 45°\), find \(\angle BAC\).

Answer: C

The exterior angle of a triangle is equal to the sum of the two opposite interior angles.

Here, \(\angle ACD\) is the exterior angle, and \(\angle ABC\) and \(\angle BAC\) are the interior opposite angles.

\(\angle ACD = \angle ABC + \angle BAC\)

120° = 45° + \(\angle BAC\)

\(\angle BAC = 120° - 45° = 75°\).

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