Số đường thẳng là
(n - 1) + (n - 2) + (n - 1) + ... + 2 + 1 = 120
Có n - 1 số hạng
(n - 1 + 1)(n - 1): 2 = 120 => n(n + 1) = 240 => n = 16
ĐS : 16
Ta có n(n-1):2=120.
n(n-1)=120.2.
n(n-1)=16.15
Vậy n=16
ta có n(n-1):2=120
n(n-1) =120.2
n(n-1) = 240=2^4.3.5
n(n-1) =16.15
vay n=16
Huỳnh Ngọc Hưng: Vì n(n-1) phải là hai số tự nhiên liên tiếp nhau
ta có n(n-1) / 2 =120
n(n-1) =120.2
n(n-1) =240 =24*3*5
n(n-1) =16*15
vậy n =16
tại sao bằng 16 * 15 ko hiểu chi hết
dap an la16 chac chan dung 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000%
đáp án là 16 chắc chắn 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000% luôn
adu nguyễn quôc anh chơi ngọc rồng ak tui cũng zậy nè .
Với n điểm, số đường thẳng vẽ được là: n x (n - 1) : 2
Theo bài ra ta có: n x (n - 1) : 2 = 190
Hay: n x (n - 1) = 190 x 2 = 20 x 19
Vậy: n = 20
