Comment Comment by rak1507 You definitely don't need to know any of that background to be able to arrive at the answer. To fully understand everything maybe, but all it takes is:a = x^1 + x^4 + x^7 + ... = x(1 + x^3 + x^6 + ...) = x/(1-x^3)a + a^3 + a^5 + ... = a(1 + a^2 + a^4 + ...) = a/(1-a^2)Substitute + simplify. I don't think this is beyond a (fairly smart) elementary school student. parent rak1507 1 year ago
a = x^1 + x^4 + x^7 + ... = x(1 + x^3 + x^6 + ...) = x/(1-x^3)
a + a^3 + a^5 + ... = a(1 + a^2 + a^4 + ...) = a/(1-a^2)
Substitute + simplify. I don't think this is beyond a (fairly smart) elementary school student.