Question

In triangle ABC, a=31 , b=22 , c=18. Identify m∠A rounded to the nearest degree.

Answer 1

Answer:

101

Step-by-step explanation:

According to the Law of Cosines, for any △ABC with side lengths a, b, and c, a2=b2+c2−2bccosA; b2=a2+c2−2accosB; and c2=a2+b2−2abcosC

.

The Law of Cosines can be used because all three side lentghs are known.

Set up the equation for the Law of Cosines:

a2=b2+c2−2bccosA

Substitute the known values into the Law of Cosines:

312=222+182−2(22)(18)cosA

Square the values and multiply:

961=484+324−792cosA

Add:

961=808−792cosA

Subtract 808

from both sides:

153=−792cosA

Divide both sides by −792

:

153−792=cosA

According to this equation m∠A

is equal to the inverse cosine function of −153792

. Write this:

m∠A=cos−1(−153792)

Calculate the value of the inverse cosine −153792

on a calculator:

m∠A≈101°

Therefore, m∠A≈101°

.