on donne sin a 4 sur 5 sans calculer la valeur de a calculer cos a

[tex]sin(a) = \frac{4}{5}[/tex]

[tex]cos^2(a) + sin^2(a) = 1[/tex]

[tex]cos^2(a) = 1 - sin^2(a) [/tex]

[tex]cos^2(a) = 1 - (\frac{4}{5})^2[/tex]

[tex]cos^2(a) = 1 - \frac{16}{25}[/tex]

[tex]cos^2(a) = \frac{25}{25} - \frac{16}{25}[/tex]

[tex]cos^2(a) = \frac{9}{25}[/tex]

[tex]cos(a) = \frac{\sqrt{9}}{\sqrt{25}}[/tex]

[tex]cos(a) = \frac{3}{5} = 0,6[/tex]


En espérant t'avoir aidé.