Question

Calcule x, sendo 3.Cx,2=45

Answer 1

3.Cx,2=45

3.x(x-1)/2!=45

3x² -3x -90=0 ===> :(3)

x² - x -30 = 0

∆= 1+120= 121 => √∆=11

x' = -b+√∆/2a = 1+11/2 = 12/2 = 6 ✓

Answer 2

Resposta:

x = 6

Explicação passo-a-passo:

Cn,p = n!/p!(n - p)!

3Cx,2 = 45

Cx,2 = 45/3

Cx,2 = 15

x!/2!(x-2)! = 15

x(x - 1)(x -2)!/2(x 2)! = 15

x(x - 1) = 30

x² - x - 30 = 0

Δ = (-1)² - 4.1(-30)

Δ 1 + 120

Δ = 121

x =  [-(-1) - 11)/2.1

x = [1 - 11)/2

x = -10/2

x = - 5 ( não serve)

ou

x = [-(-1) + 11]/2

x = (1 + 11)/2

x = 12/2

x = 6