cho n duong thang doi mot giao nhau va khong co giao diem nao thuoc 3 duong thang. biet rang so giao diem tao ra boi n duong thang gap 10 lan so duong thang. 1 bo ba diem A,B,C
goi la bo tot neu giua A va C chi co dung B trong cac giao diem cua n duong thang co it nhat bao nhieu bo tot
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tren mat phang cho n duong thang trong do bat ky hai duong thang nao cung cat nhau va khong co ba duong thang nao cung di qua mot diem. biet rang tong so giao diem ma n duong thang do tao ra bang 465.tim n
Cho n duong thang trong do bat cu hai duong thang nao cung cat nhau,khong co ba duong thang nao cung di qua 1 diem.
a)Biet rang so giao diem cua cac duong thang do la 1128 . Tinh n.
b)So giao diem cua cac duong thang do co the la 2017 duoc khong?Vi sao?
a)ta có: n.(n-1) :2 = 1128
=> n.(n-1)= 1128.2= 2256= 2^4.3.47= 48.47
vậy n = 48
b) n.(n-1) :2 = 2017
=> n.(n-1)= 2017.2= 4034=2.2017
vì 2017 là số nguyên tố nên 4034 không thể phân tích được thành tích của hai số tự nhiên liên tiếp
vậy số giao điểm của các đường thẳng đó không thể là 2017
Bai 1:Cho n duong thang (n>2) doi mot cat nhau va ko co 3 duong thang nao cung di qua mot diem. Hoi so giao diem n duong thang noi tren co the la 2014 duoc ko?
Bai 2; ve 4 duong thang phan biet va cat nhau doi mot.So giao diem co the la bao nhieu?
1. Tren 1 duong thang xy lay 4 diem phan biet A,B,C,D hay chi ra cac tia doi nhau
2. cho 10 diem trong do khong co ba diem thang hang . Cu qua hai diem ta ve duoc 1 duong thang . Hoi co tat ca bao nhieu duong thang?
3. cho n diem trong do khong co ba diem nao thang hang . Cu qua hai diem trong so cac diem do ve duoc 1 duong thang. Biet rang co 435 duong thang tao thanh .Tim n?
cho n duong thang ( n lon bang 2 )trong do 2 duong thang nao cung cat nhau , khong co 3 duong thang nao dong quy
a. tinh so giao diem neu n= 4
b.tinh so giao diem theo n
a ) vì trong 4 đường thẳng không có 3 đường thẳng nào đồng quy nên 1 đường thẳng cắt 3 đường thẳng còn lại tạo thành 3 giao điểm
có 4 điểm nên có 4 x 3 = 12 giao điểm
vì số giao điểm được tinh 2 lần nên số giao điểm là 12: 2 = 6 giao điểm
b) tương tự với bài trên có{ n x (n-1) } : 2 giao điểm
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cho 5 duong thang phan biet doi mot cat nhau, khong co 3 duong thang nao cat nhau tai 1 diem .hoi co bao nhieu giao diem
Cho truoc mot so duong thang phan biet khong co 3 diem nao thang hang. So duong thang tao thanh tu cac diem do la 36, tinh so diem ?
Cau 5: Trong cac khang dinh sau, khang dinh nao dung, khang dinh nao sai?1.Ba diem phan biet la ba diem thang hang.2.Voi ba diem phan biet luon co hai diem nam ve cung phia doi voi diem con lai.3.Voi ba diem thang hang phan biet luon co hai diem nam khac phia voi diem con lai.4.Voi ba diem A,B,C thang hang thi diem B luon nam giua hai diem A,C.5.Co mot va chi mot duong thang di qua hai diem (phan biet) cho truoc.6.Hai duong thang phan biet thi song song voi nhau.7.Hai tia chung goc thi cung nam...
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Cau 5: Trong cac khang dinh sau, khang dinh nao dung, khang dinh nao sai?
1.Ba diem phan biet la ba diem thang hang.
2.Voi ba diem phan biet luon co hai diem nam ve cung phia doi voi diem con lai.
3.Voi ba diem thang hang phan biet luon co hai diem nam khac phia voi diem con lai.
4.Voi ba diem A,B,C thang hang thi diem B luon nam giua hai diem A,C.
5.Co mot va chi mot duong thang di qua hai diem (phan biet) cho truoc.
6.Hai duong thang phan biet thi song song voi nhau.
7.Hai tia chung goc thi cung nam tren mot duong thang.
8.Hai tia chung goc thi doi nhau
9.Neu diem M nam giua diem A,B thi no la trung diem cua doan thang AB.
10.Neu MA=MB thi M la trung diem cua doan thang AB.
11.Neu MA+MB= AB va MA=MB thi M la trung diem cua doan thang AB.
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ve 2017 duong thang doi 1 cat nhau va khong co 3 duong thang nao dong quy. hoi co bao nhieu giao diem duoc tao thanh.