Question

ex 2 si 4 va rog ofer puncte!!!

Answer 1

Răspuns:

Explicație pas cu pas:

2) a)

S = (-3) + (-2) + (-1) +.......+ (+25) + (+26) + (+27)

S = (0+1+2+3+...+24) + (27-3) + (26-2) + (25-1)

S = (1+24)·24:2 + 24·3

S = 25·12 + 72 = 300 + 72

S = 372

2) b)

I 2z -1 I = 3 ; z ∈ Z

2z - 1 = 3 => 2z = 4 => z = 2 ∈ Z

-2z+1 = 3 => 2z = -2 => z = -1 ∈ Z

z ∈ {-1 ; 2}

4)a)

4 - 3x = 25 => 3x = 4-25 => 3x = -21 =>

x = -21:3 => x = -7 ∈ Z

4)b)

6 - 2x ≤ -16 <=>

6+16 ≤ 2x <=>

22 ≤ 2x   I : 2 =>

11 ≤ x =>

x ≥ 11  I x ∈ Z =>

x ∈ {11 ; 12 ; 13 ; ..........}