If a is the third quadrant angle, Sina + cosa = 5 / 9, sin2a =?
sina2a=2sina*cosa
(sina+cosa)*(sina+cosa)=25/81=1+2sinacosa=1+sin2a
sin2a=-56/81
If a is the angle of the third quadrant, what is [√ (1 + sin2a)] / Sina + cosa,
[√(1+sin2a)]/sina+cosa
=[√ (Sina + COSA) square] / Sina + cosa
=-(sina+cosa)/(sina+cosa)
=-1