Question

Determinati elementele multimii :
D={x€ Z| x-1€ D20}

Answer 1

D₂₀ ={ 1 ; 2 ; 4 ;5 ; 10 ; 20 } 
x -1 = 1 ; x =2
x -1 = 2  ; x =3 
x -1 =4  ;  x =5 
x -1 = 5  ; x = 6 
x -1 = 10 ; x =11 
x  -1 = 20 ; x =21
D = { 2 ;3 ;5 ;6 ;11 ;21 }

Answer 2

$x-1 \in D_{20} \Longrightarrow x-1 \in \{1, 2, 4, 5, 10, 20\}|_{+1} \Longrightarrow x \in \{2,3,5,6,11,21\}$