Question

Please explain and help set up

Answer 1

D

using the Cosine rule in ΔABC

let a = BC, b = AC and c = AB, then

b² = a² + c² - (2ac cosB )

substitute appropriate values into the formula

b² = 7² + 9² - (2 × 7 × 9 × cos 73° )

= 49 + 81 - 126 cos 73°

= 130 - 36.84 = 93.16

⇒ b =
`√(93.16)` ≈ 9.7 → D