cos a = 1 - 5/13*5/13=12/13*12/13
tg a = sin a / cos a =(5/13*5/13)/(12/13*12/13) = 5/13*5/13*13/12*13/12 = 5/12*5/12
cos a = 1 - 5/13*5/13=12/13*12/13
tg a = sin a / cos a =(5/13*5/13)/(12/13*12/13) = 5/13*5/13*13/12*13/12 = 5/12*5/12