sina=sqr(1-(cosa)^2)=sqr(1-(12/13)^2)=sqr(1-144/169)=sqr(25/169)=5/13
169=x^2+144
x^2=25
x=5
sina=5/13
sina=sqr(1-(cosa)^2)=sqr(1-(12/13)^2)=sqr(1-144/169)=sqr(25/169)=5/13
169=x^2+144
x^2=25
x=5
sina=5/13