Quadratic Trigonometric Equations (Edexcel A-Level Mathematics): Quizzes

$a \cdot (\text{trig})^2 + b \cdot (\text{trig}) + c = 0$

Let $u = \sin\theta$ and substitute

$(2u + 1)(u - 1) = 0$

$\cos\theta$ must be between $-1$ and $1$

$\theta = 90°, 210°, 330°$

$u = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$

$\theta = 60°, 120°, 240°, 300°$

$0°$ to $360°$ or $0$ to $2\pi$ radians

$\sin^2(\theta)$

$\cos\theta = 1$ only