Question 1197887


use the law of cosines 

{{{cos(C) = (a^2 + b^2 - c^2)/(2ab)}}}

{{{cos(C) = (6^2 + 8^2 - 13^2)/(2*6*8)}}}

{{{cos(C) = -69/96}}}

{{{cos(C) = -23/32}}}

{{{C = cos^-1(-23/32)}}}

{{{C = 2.3727991}}} rad. or  {{{C = 136}}}°