Triangle $ABC$ has $AB=7$ cm, $AC=9$ cm and $BC=12$ cm. A pupil suggests using the sine

Question

Triangle $ABC$ has $AB=7$ cm, $AC=9$ cm and $BC=12$ cm. A pupil suggests using the sine rule first to find $\angle BAC$. Explain why the cosine rule is a useful first step here.[1] Calculate $\angle BAC$, correct to 1 decimal place.[3]

Accepted Answer

(a) Three sides are known and no angle is known (b) $96.4^\circ$

Choosing a rule from the givens

Choosing a rule from the givens

Solution:

Solution locked