daca ducem SS` _|_ PQ si RR` _|_ PQ avem
in ΔPSS`,∧PSS`=120-90=30*
daca notam PS=SR=x si PQ=3x
conform th unghiului de 30*
PS`=PS/2=x/2
SS`=RR`
sin SPS`=SS`/SP
sin 60*=SS`/x=√3/2
SS`=x√3/2
QR`=3x-x/2-x=3x/2
tg RQR`=x√3/2:3x/2=x√3/2.2/3x=√3/3
inseamna ca ∧RQR`=30*