Question

Aratati ca sin(a+b)=63/65 stiind ca sin a=3/5 si sin b = 12/13
Chiar m-am blocat aici

Answer 1

Avem formula: sin(a+b)=sinacosb+sinbcosa
cosa=+sau- $\sqrt{1-sin^2a}$=+sau- 4/5, analog cosb=+ sau-5/13
 deci: sin(a+b)=3/5×5/13+12/13×4/5=63/65, daca a si b ∈(0,π/2) sau in cadranul I in caz contrar se obtin alte valori !