Kąt [latex] alpha [/latex] jest kątem ostrym i cos [latex] alpha = frac{2}{3} [/latex] . Ile wynosi sin [latex] alpha [/latex] ?

[latex]0^{o} extless alpha extless 90^{o}\cos alpha = frac{2}{3}\\sin^{2}alpha + cos^{2}alpha = 1\\sin^{2}alpha = 1-cos^{2}alpha = 1 - (frac{2}{3})^2}} = frac{9}{9}-frac{4}{9}+ frac{5}{9}\\sinalpha = sqrt{frac{5}{9}} =frac{sqrt{5}}{sqrt{9}} = frac{sqrt{5}}{3}[/latex]