Question

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 ?

 

Answer 1

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Answer 2

 105 = n.(n-1):2

=n.(n-1)=105.2

=n.(n-1)=210

=n.(n-1)=15.14

vậy n = 15

Answer 3

ta co 105=n[n-1]chia 2

210=n[n-1] 

14.15=n[n-1]

vay n=15