a) Số đường thẳng là :
\(\frac{n.\left(n-1\right)}{2}=\frac{100.99}{2}=4950\) (đường thẳng)
b) Ta có n.(n - 1) : 2 = 378
=> n.(n - 1) = 756 = 28 . 27 = 28 . (28 - 1)
Vậy n = 28
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 diem trong do ko co 3 diem nao thang hang . cu qua 2 diem ta ve duoc 1 duong thang . biet rang co tat ca 105 duong thang . tinh n?
cho n diem trong do khong co 3 diem nao thang hang . Cu qua 2 diem ta ve 1 duong thang . Biet rang co tat ca 105 duong thang . tim n ?
bai1 cho n diem trong do khong co 3 diem nao thang hang .Cu qua 2 diem ta ve mot duong thang biet rang co tat ca 105 duong thang .Tinh n
Bai 1: Cho 60 diem trong do co 15 diem thi cu qua 2 diem ve duoc 1 duong thang . Hoi ve duoc bao nhieu duong thang ? Bai 2:Cho n diem ko co 3 diem nao thang hang cu qua 2 diem ve duoc 1 duong thang . Biet ve duoc 28 duong thang . Tinh so diem n ?
cho truoc n diem trong do k co 3 diem nao thang hang ve duong thang di qua cac cap diem. Tim n biet rang neu co them 1 diem (k thang hang voi bat cu 2 diem nao trong tong so n diem da cho) thi so duong thang ve dc tang them 8 duong
cho 100 diem , trong do khong co 3 diem nao thang hang . cu qua hai diem ta ve duoc 1 duong thang . hoi co bao nhieu duong thang ?
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?
cho 15 diem phan biet (trong do ko co 3 diem nao thanh hang) ,cu qua hai diem ve duoc 1 duong thang. tinh so duong thang di qua cac cap diem
