Question

If in oblique ΔABC
Δ
𝐴
𝐵
𝐶
side a=13
𝑎
=
13
m, side b=6
𝑏
=
6
m, and side c=9
𝑐
=
9
m, then use the Law of Cosines to find the measure of ∠A
∠
𝐴
.(1 point)
Responses

63 degrees
63 degrees

15 degrees
15 degrees

50 degrees
50 degrees

119 degrees
119 degrees

Answer 1

Use the Law of Cosines:
cos A = (b^2 + c^2 − a^2) / (2bc) = (6^2 + 9^2 − 13^2) / (2·6·9)
= (36 + 81 − 169) / 108 = −52/108 = −13/27.

A = arccos(−13/27) ≈ 119°.

Answer: 119 degrees.