5. Multimea A

D (14) = 1, 2, 7, 14

=> 2x +1 = 1, 2, 7, 14

=> 2x = 0, 1 (nu convine), 6 , 13 (nu convine)

=> A = ( 0 si 3 )

Multimea B

(3X + 5  / 2 X + 1 )  + 1

3 X x 2 / 2 X x 2  

simplificam 2 x X =>  3 / 2 = 3 jumatati

Multiplii comuni 2 si 3: 6, 12, 18, 24, 30 ...

6 : 3 jum. / 2 = 1 unitate => convine

12 : 3 jum / 2 = 2 unitati , 12 : 2 = 6

A = (Multiplii 2 si 3)

Multimea C

x = toate nr cuprinse intre 51 si 61

A = ( 60, 59, 58, 57, 56, 55, 54, 53, 52)

Multimea D

(5 / 6 ) x 2 <sau egal X + 1 / 12 < ( 5 / 4 ) x 3

=> 10 / 12 <sau egal X + 1 / 12 < 15 / 12

=> X = 9, 10, 11, 12, 13

6.  Deocamdata nu stiu, scz

7.  ab0 - ab = 10 x ab - 1x ab = 9 x ab

9 x ab / 9 = ab