4 A triangle ABC has sides \(\mathrm { AB } = 5 \mathrm {~cm} , \mathrm { AC } = 9 \mathrm {~cm}\) and \(\mathrm { BC } = 10 \mathrm {~cm}\).
- Find the cosine of angle BAC, giving your answer as a fraction in its lowest terms.
- Find the exact area of the triangle.