Răspuns
Explicație pas cu pas:
a) Fie AH⊥BC => AH=d(A, BC)
∡B≡∡D=30° (opuse in paralelogram) ;
in ΔABH (∡H=90°) AH-cateta opusa ∡ de 30° => AH=1/2AB => AH=5cm
=> d(A, BC)=5cm.
b) Aria paralelogram=baza·inaltimea;
daca AH⊥ABC => AH-inaltime
baza BC=AD =8cm (laturi opuse in paralelogram)
=> Aria ABCD=BC·AH
=> Aria ABCD=8·5=40cm²