Page 76 - Engineering
P. 76
ﺍﳌﺜﻠﺜﺎﺕ ٦٣
AD
BC
أﻧﺸﺊ اﳌﺴﺘﻄﻴﻞ .ABCDﻣﻦ اﻟﻮاﺿﺢ أن .△ABC ≡ △CDAوﳍﺬا
] .[ABC ] = [CDAإذن،
] [ABC = ] 1 [ABCD = ) 1 (AB)(BC = 1 aha
2 2 2
ﻟﻨﻔﺮض اﻵن أن اﳌﺜﻠﺚ △ABCﺣﺎد اﻟﺰواﻳﺎ
A
ha
B DC
] [ABC ] = [ABD] + [ADC
= 1 (BD)ha + 1 (DC )ha
2 2
= 1 (BD + DC )ha
2
= 1 (BC )ha
2
= 1 aha
2
وأﺧﲑاً ﻧﻔﺮض أن △ABCﻣﻨﻔﺮج اﻟﺰاوﻳﺔ