Fie x, y măsurile celor două unghiuri.
[tex]\it x+y=90^o\ \ \ \ (*)\\ \\ \{x,\ y\}\ i.\ p\ \{4,\ 5\} \Rightarrow 4x=5y|_{+5x} \Rightarrow 9x=5x+5y \Rightarrow\\ \\ \Rightarrow 9x = 5(x+y)\stackrel{(*)}{\Longrightarrow} 9x=5\cdot90^o|_{:9} \Rightarrow x=50^o\\ \\ x=50^o\stackrel{(*)}{\Longrightarrow} 50^o+y=90^o \Rightarrow y=40^o[/tex]
