Répondre :
[tex]cos(a) = 0,6[/tex]
[tex]cos^2(a) + sin^2(a) = 1[/tex]
[tex]sin^2(a) = 1 - cos^2(a) [/tex]
[tex]sin^2(a) = 1 - 0,6^2[/tex]
[tex]sin^2(a) = 1 - \frac{6^2}{10^2}[/tex]
[tex]sin^2(a) = \frac{100}{100} - \frac{36}{100}[/tex]
[tex]sin^2(a) = \frac{64}{100}[/tex]
[tex]sin(a) = \frac{\sqrt{64}}{\sqrt{100}}[/tex]
[tex]sin(a) = \frac{8}{10} = \frac{4}{5} = 0,8[/tex]
En espérant t'avoir aidé.