Odpowiedź :
[tex]sin^2\alpha+cos^2\alpha=1\\\\(\frac{9}{41})^2+cos^2\alpha=1\\\\\frac{81}{1681}+cos^2\alpha=1\\\\cos^2\alpha=1-\frac{81}{1681}\\\\cos\alpha=\frac{1600}{1681}\\\\cos\alpha=\sqrt{\frac{1600}{1681}}\\\\cos\alpha=\frac{40}{41}[/tex]
[tex]sin^2\alpha+cos^2\alpha=1\\\\(\frac{9}{41})^2+cos^2\alpha=1\\\\\frac{81}{1681}+cos^2\alpha=1\\\\cos^2\alpha=1-\frac{81}{1681}\\\\cos\alpha=\frac{1600}{1681}\\\\cos\alpha=\sqrt{\frac{1600}{1681}}\\\\cos\alpha=\frac{40}{41}[/tex]