Question

How to do this do i have to use Cosine law ?

Answer 1

4.9 cm

Explanation:

Given:

a = 8.2cm

B = 31°

A = 90° - 31° = 59°

We calculate the length of side b by means of the law of sines, as follows:

`\begin{gathered} (a)/(\sin A)=(b)/(\sin B) \\ \\ \text{ We replacing:} \\ \\ (8.2)/(\sin59)=(b)/(\sin31) \\ \\ b=8.2\cdot(\sin31)/(\sin59) \\ \\ b=4.9\text{ cm} \end{gathered}`

The length of side b is 4.9 cm