Question

PLEASE HELP!!
In triangle ABC, B= 120 degrees, a=10, c=18, find C

Answer 1

add all of them then subtract from 180

Answer 2

check the picture below. Notice that we can always solve for the cosine and simply use the sides alone to get an angle.


`\bf cos^(-1)\left(\cfrac{10^2+(√(604))^2-18^2}{2(10)(√(604))} \right)=\measuredangle C \\\\\\ cos^(-1)\left(\cfrac{100+604-324}{20√(604)} \right)=\measuredangle C \\\\\\ cos^(-1)(0.77309903583)\approx \measuredangle C\implies 39.366998916677^o\approx \measuredangle C`