law of cosine trig

Question

Find the missing side or angle. Round to the nearest tenth.

c=5

b=4

a=2

B=?

Answer 1

Have you tried using the law of cosines?

b² = a² + c² - 2ac*cos(B)

Answer 2

using the law of cosines...

b^2=a^2+c^2-2ac(cosB)

16=4+25-2*2*5*cosB

16=29-20*cosB

16-29=-20*cosB

-13=-20*cosB

-13/(-20)=cosB

13/20=cosB

0.65=cosB

cos^-1B=0.65

use your calculator or use the web to find arccos finder

∠B=49.45839813º

∠B=49º 27' 30.233"

∠B=49.5° to the nearest tenth