## Trigonometry (11th Edition) Clone

$\theta=15^{\circ}$
Since sine and cosine are cofunctions, $\sin(\theta+15^{\circ})= cos (2\theta+30^{\circ})$ is true if the sum of the angles is 90°. $(\theta+15^{\circ})+(2\theta+30^{\circ})=90^{\circ}$ $3\theta+45^{\circ}=90^{\circ}$ Subtracting $45^{\circ}$ from each side, $3\theta=45^{\circ}$ Dividing each side by $15$, $\theta=15^{\circ}$