Originally Posted by

**william** I have to solve a triangle

the given information in triangle ABC is c=28.6,b=19.9 and A=48.1^o

i used the cosine law to get a which i found to be 21.3 is this correct?

i then tried to use the cosine law again to find one of the other angles

my work:

$\displaystyle

c^2=a^2+b^2=2ab CosC$

$\displaystyle

28^2=21.3^2+19.9^2-2(21.3)(19.9)CosC$

$\displaystyle

CosC=\frac{28.6^2-21.3^2-19.9^2}{-2(21.3)(19.9)}$

$\displaystyle

CosC= \frac{-31.74}{-822.18}$

$\displaystyle CosC=sin^{-1} 0.038$

$\displaystyle C= 87^o$

is this right? i don't think it is because we are working with obtuse triangles