Trójkąt prostokątny ma boki o długościach:
a = 2√5, b = √5, c = 5,
Zauważmy, że a² +b² = c², bo
(2√5)² + (√5)² = 4*5 + 5 = 5*5 = 5²
sinα = b/c = √5/5
cos α = a/c = (2√5)/5
tg α = b/a = √5/(2√5) = 1/2
ctg α = a/b = (2√5)/(√5) = 2
sin β = a/c = (2√5)/5
cos β = b/c = √5/5
tg β = a/b = 2
ctg β = b/a = 1/2
