Since r will always be < 1 for every n >= 1, I tried to resolve a / (1 - r), but I never got 3/4.
Thinking I had to set a equal to "1/3", I did not get 3/4 either.
Then, I told myself it was a combinaison of two series :
1. 1 / n2
2. 1 / 2n
But the second one does not have a limit since it is 1 / 2 multiplied by the harmonic series (1 / n) which does not converge.
What am I doing wrong ? What did I not see ?
I just started this calculus class in university and my college maths are soooooooo far away (11 years).
Thanks for your help