Question 769551
{{{tan(alpha)=12/5)}}}

so in III

{{{r=sqrt(12^2+5^2)=13}}}
{{{sin(alpha)=-12/13}}}
{{{cos(alpha)=-5/13}}}

in II

{{{sin(beta)=sqrt(1-(-20/29)^2)=21/29}}}


{{{sin(alpha+beta)=sin(alpha)cos(beta)+cos(alpha)sin(beta)}}}


{{{sin(alpha)cos(beta)+cos(alpha)sin(beta)=(-12/13)(-20/29)+(-5/13)(21/29)=135/377}}}