Question

Resolva essa questão pra mim C n,2=105 (combinação)

A)21
B) 12
C)15
D)35

Answer 1

Combinacao :
__________
C(n,2) = 105

Formula e :
n(n-1) = 105
____
...2!

resolvendo
n^2 - n = 105
_____
.....2

n^2 - n = 105 x 2
n^2 - n = 210
n^2 - n + 210 = 0
a=1....b= -1...c= - 210
formula de Delta
D = b^2 - 4 a c
D = (-1)^2 - 4 (1)(-210)
D = 1 - 4(- 210)
D = 1 + 840
D = 841
formula de Brakara
n = - b +,- \/ D
....._________
............2a

n = - (- 1) +,- \/841
......___________
................2(1)

n = 1 +,- 29
......______
..........2

n' = 1 + 29
......______
............2

n' = 30
......___
.........2

n' = 15..Ok

n" = 1 - 29
......._____
...........2

n" = - 28
.......____
...........2

n" = - 14 (descartado porque e negativo)

RESPOSTA e a alternativa C)15