Question

In △ABC,a=14, b=17, and c=22. Find m∠A.

Answer 1

Answer:

$\large\boxed{m\angle A\approx39^o}$

Step-by-step explanation:

Use the cosine law:

$a^2=b^2+c^2-2bc\cos A$

We have:

$a=14,\ b=17,\ c=22$

Substitute:

$14^2=17^2+22^2-2(17)(22)\cos A\\\\196=289+484-748\cos A\\\\196=773-748\cos A\qquad\text{subtract 773 from both sides}\\\\-577=-748\cos A\qquad\text{divide both sides by (-748)}\\\\\cos A=\dfrac{577}{748}\\\\\cos A\approx0.7714\to m\angle A\approx39^o$