Question

Use 1/2ab sin C formula pls

Answer 1

Explanation:

`area = (1)/(2) a.b \sin(C) \\ from \:cosine \: rule \\ {c}^(2) = {a}^(2) + {b}^(2) - 2a.b \cos(C) \\ 36 = 144 + 81 - (2 * 12 * 9) \cos(C) \\ 189 = 216 \cos(C) \\ \cos(C) = 0.875 \\ C = \cos {}^( - 1) (0.875) \\ C = 28.96 \degree \\ area = (1)/(2) * 144 * 9 * \sin(28.96 \degree) \\ area = 313.8 \: sq \: units`