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2014-05-24T01:15:11+03:00
ΔABC
M∈[AB]
N∈[AC]
MN ||AC     ⇒ΔAMN ≈ΔABC   ⇒AM/AB=MN/BC=AN/AC

⇔8/12= MN/15 =AN/18

8/12=MN/15  ⇒MN= 15*8/12=  15*2/3=  5*2=10   MN=10

8/12 =AN/18  ⇒AN=8*18/12=  8*3/2= 4*3=12   AN=12

PΔAMN=8+12+10= 20+10=30cm
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