Question

A)X-1 € D15
B) 2x+1 € D12
C) x+2 € D21

Answer 1

a)X-1∈{1,3,5,15} ⇒x∈{2,4,6,16}
b)2x+1∈{1.2.3.4.6.12}⇒2x∈{0.1.2.3.5.11}⇒x∈{0,1.,0.5,1.5,2.5,5.5}
c)x+2∈{1.3.7.21}⇒x∈{-1.1.5.19}