Study notes
Trigonometric Identities & Equations
Trig ratios of any angle using the CAST rule and reference angles, the Pythagorean identity, and solving trig equations over a range (including quadratics in sinθ/cosθ).
What this topic covers
- The CAST rule tells you which ratio is positive in each quadrant
- The reference angle is the acute angle to the x-axis
- The Pythagorean identity links sine and cosine of the SAME angle
- \(\tan\theta = \dfrac{\sin\theta}{\cos\theta}\) connects the third ratio to the first two
- Solving \(\sin\theta=k\) or \(\cos\theta=k\) over a range means finding EVERY solution, not just one
- A quadratic in \(\sin\theta\) or \(\cos\theta\) is solved by substitution first, THEN trig
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