Given
a=15
b=11
c=21
Find
all angles of the triangle
Explanation
Using law of cosine to find angle A
[tex]\begin{gathered} A=\cos^{-1}\lbrack\frac{b^2+c^2+a^2}{2bc}] \\ =\cos^{-1}[\frac{11^2+21^2-15^2}{2\times11\times21}] \\ =43.29 \end{gathered}[/tex]Similarly
[tex]\begin{gathered} \angle B=30.1 \\ \angle C=106.7 \end{gathered}[/tex]Final Answer
option (b) is correct
