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 ; ..........}
