How to apply the sum of angles with the sine of an angle not on unit circle

The video tutorial explains how to find the sine and cosine of angles using trigonometric identities and the Pythagorean theorem. It focuses on angles in Quadrant 3, where both sine and cosine are negative. The tutorial demonstrates how to use triangles to calculate missing trigonometric values and simplify expressions. The process involves understanding the properties of Quadrant 3, applying the Pythagorean theorem, and using given values to find unknowns.

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