For Q3, elements of A1 can be derived by putting n=1 and k=1,2,3....in A(n)=(n+1)*k, thus A1={(1+1)*1, (1+1)*2, (1+1)*3,(1+1)*4.......}={2,4,6,8,10,12,14,16,18...}, similarly A2= {3,6,9,12,15,18.......},

Thus A1 intersection A2= {6,12,18,24,........}= A5, verify putting n=5 and respective values of k with A5.

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