Question 868519
{{{sin^2(alpha)+cos^2(alpha)=1}}}
{{{(3/5)^2+cos^2(alpha)=1}}}
{{{cos^2(alpha)=1-9/25}}}
{{{cos(alpha)=0 +- 4/5}}}
Since {{{pi/2<alpha<pi}}},
{{{cos(alpha)=-4/5}}}
..
.
.
{{{cos(beta)=-12/13}}}
Similarly,
{{{sin(beta)=sqrt(1-144/169)}}}
{{{sin(beta)=0 +- 5/13}}}
Since {{{pi<beta<(3/2)pi}}}
{{{sin(beta)=-5/13}}}