Answer: 81°
Explanation:
1) Law of cosines:
In a triangle with sides a, b, c whose opposite angles are, respectively, A, B and C, the law of cosines states:
b² = a² + c² - 2 (a)(c) cos (B)
2) In the triangle of the figure you have
b = 4.0
B = ?
a = 2.2
c = 3.7
⇒ (4.0)² = (2.2)² + (3.7)² - 2 (2.2) (3.7) cos(B)
⇒ 16 = 4.84 + 13.69 - 16.28cos(B)
⇒ 16.28 cos(B) = 4.84 + 13.69 - 16 = 2.53
⇒ cos(B) = 2.53 / 16.28
⇒ X = arccos(2.53 / 16.28 ) = 81.06° ≈ 81°
