Question

AJUTORRRR DAU COROANAAAA, ESTE URGENTTT​

Answer 1

Răspuns:

Explicație pas cu pas:

n = 5C1 + 3

n = 6C2 + 3

n = 8C3 + 3

n - 3 = 5C1

n - 3 = 6C2

n - 3 = 8C3

cmmmc (5, 6, 8) = 120

n - 3 = 120

n = 120 + 3 = 123

__________________

(x + 3)/(x + 1) = (x + 1 + 2)/(x + 1) = (x + 1)/(x + 1) + 2/(x + 1) = 1 + 2/(x + 1)

2/(x + 1) trebuie sa fie numar intreg

x + 1 = -2; -1; 1; 2

x = -3; -2; 0; 1

x ∈ N ⇒ x = {0,1}

___________________

1/1*2 = 1/1 - 1/2

1/2*3 = 1/2 - 1/3

1/3*4 = 1/3 - 1/4

..............

1/2005*2006 = 1/2005 - 1/2006

S = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/2005 - 1/2006 = 1 - 1/2006

= 2006/2006 - 1/2006 = 2005/2006