Review question

# If $\sin \alpha = 3/5, \cos \beta = 12/13$, what's $\cos(\alpha + \beta)$? Add to your resource collection Remove from your resource collection Add notes to this resource View your notes for this resource

Ref: R9740

## Suggestion

Given that $\sin \alpha = \dfrac{3}{5}$ and $\cos \beta = \dfrac{12}{13}$, prove that one possible value of $\cos(\alpha + \beta)$ is $\dfrac{33}{65}$

Could we draw a diagram with right-angle triangles and the angles $\alpha$, $\beta$ and $\alpha+\beta$?

If two sides of a right-angle triangle are $3$ and $5$, what is the third side?