1. Sina+cosa=1/3
(Sina+cosa)²=sin²a+cos²a+2 sina cosa=1+sin2a
(1/3)²=1+sin2a
Sin2a=1/9-1=-8/9
Raspuns: sin2a=-8/9
2. In cadranul 2, sina=3/5. Cosa este negativ.
Cos²a=1-sin²a=1-(3/5)²=1-9/25=16/25
Deci cosa=-4/5.
Tga=sina/cosa=(3/5)/(-4/5)=-3/4.
Raspuns: tga=-3/4
