Fie t= triunghiuri, p=patrate, d=dreptunghiuri.
t+p+d= 16
3t+4p+4d= 60 unghiuri (triunghiul are 3, patratul si respectiv dreptunghiul, au 4unghiuri)
d= 3p
t+p+3p= 16 => t+ 4p= 16
3t+4p+4*3p= 60 => 3t+ 16p= 60
[tex] \left \{ {{t+4p= 16} | *(-3) \atop {3t+16p=60}} \right. [/tex]
[tex] \left \{ {{ -3t-12p=-48} \atop {3t+16p=60}} \right. [/tex]
[tex]-4p= 12 =\ \textgreater \ p= 3 (patrate) [/tex]
[tex]d=3p=3*3=9(dreptunghiuri)[/tex]
[tex]t= 16-(9+3)= 4(triunghiuri )[/tex]
