Question

Use the Law of Sines to find the missing angle of the triangle.

Answer 1

Answer:

m∠B = 70.0° (nearest tenth)

Step-by-step explanation:

Sine Rule for Angles

$\sf \dfrac{\sin A}{a}=\dfrac{\sin B}{b}=\dfrac{\sin C}{c}$

(where A, B and C are the angles and a, b and c are the sides opposite the angles)

Given:

• a = 13
• c = 19
• A = 40°

Substituting the given values into the formula to find m∠C:

$\implies \sf \dfrac{\sin 40^{\circ}}{13}=\dfrac{\sin C}{19}$

$\implies \sf \sin C=\dfrac{19\sin 40^{\circ}}{13}$

$\implies \sf C=\sin^{-1}\left(\dfrac{19\sin 40^{\circ}}{13}\right)$

$\implies \sf m \angle C=69.96086904^{\circ}$

Interior angles of a triangle sum to 180°

$\implies \sf m \angle A+ m \angle B+m \angle C=180^{\circ}$

$\implies \sf 40^{\circ} + m \angle B+69.960...^{\circ}=180^{\circ}$

$\implies \sf m \angle B=70.03913...^{\circ}$

Therefore, m∠B = 70.0° (nearest tenth)