Hi.

It is ,

what is n? n = 0 or n = 1/2 or n = 1 or n = 3/2 or n = 2 or ... or n = 5

It should be

Check it for all n

n= 0:

2*0+1 = 1, is ? Yes it is! Therefor our solution contains 2*0+1 = 1

n = 1/2 :

2*1/2 + 1 = 2,

is 2 in A? Yes it is, therefor 2 is a solution, too

...

...

...

n = 5:

2*5 + 1 = 10+1 =11

Is 11 in A? No, its not! Therefore 11 is not a solution.

Do you think you find the other solutions by yourself?

Regards, Rapha