Question 856550
Since it's on the unit circle,
{{{x^2+y^2=1}}}
{{{(5/13)^2+y^2=1}}}
{{{25/169+y^2=169/169}}}
{{{y^2=144/169}}}
{{{y=0 +- 12/13}}}
Since it's in Q4, it's the negative value.
{{{y=-12/13}}}