Sinus kąta ostrego α\alphaα jest równy 45\small \displaystyle \frac{4}{5}54. Wtedy
cosα=54\cos \alpha = \small \displaystyle\frac{5}{4}cosα=45
cosα=15\cos \alpha = \small \displaystyle\frac{1}{5}cosα=51
cosα=925\cos \alpha = \small \displaystyle\frac{9}{25}cosα=259
cosα=35\cos \alpha = \small \displaystyle\frac{3}{5}cosα=53