b) A drept.ABCD = L· l = 30 · 20 = 600 cm²
A Δ DNM = 600 / 3 = 200 cm²
⇒ A Δ AND + A Δ NBM + A Δ CDM = 400 cm²
⇒ AN ·AD / 2 + MB ·NB / 2 + 150 = 400
⇒ 20 AN /2 + 10 NB / 2 + 150 = 400
⇒ 10 AN + 5 NB = 400 -150
⇒ 10 AN + 5 NB = 250
⇒ 2 AN + NB = 50
Cum AN + NB = 30
Avem :
2 AN + NB = 50
AN + NB = 30 (sistem de 2 ecuatii cu 2 nec:)
2 AN + NB =50
-AN - NB = - 30 ( am inmultit cu -1)
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AN = 20 (cm)
