Notam DC = x
Aplicam T.catetei in triunghiul abc => 40² = DC × BC => 1600= x(18+x) => 1600 = x² + 18x
Adaugam 81 => 1681 = x² +18 x +81
1681= (x+9)² => x+9 = 41 sau - 41
=> x= 32cm sau -50 dar cum x este lungimea unei laturi => x=32cm => BC=50cm => T.Pitagora AB=30cm
Perimetru = 30+50+40=120cm
A=30×40/2 = 600cm²