Question

Determinati valorile intregi ale lui x, astfel incat 21pe 2x+1 sa fie numar intreg!
Va rogg repedee

Answer 1

Daca 21\ 2x+1 ∈ Z ⇒ 21 divide 2x+1, adica 2x+1 ∈D₂₁⇒2X+1∈ { -1; -3; -7; -21; 1; 3; 7; 21 }
2X+1=-1⇒2x=-2⇒x=-1
2x+1=-3⇒2x=-4⇒x=-2
2x+1=-7⇒2x=-8⇒x=-4
2x+1=-21⇒2x=-22⇒x=-11
2x+1=1⇒2x=0⇒x=0
2x+1=3⇒2x=2⇒x=1
2x+1=7⇒2x=6⇒x=3
2x+1=21⇒2x=20⇒x=19

x∈ { -11; -4; -2; -1; 0; 1; 3; 19 }