# Make Mathematica expanding a series [closed]

I've just started with Mathematica and I'm still learning the basics.

At the moment I want Mathematica to display series multiplication in this form, so I can investigate generating functions better. $c(x)$ is an infinite series, but I just want to look at a few terms in the multiplication.

How do I do it? I got to here but couldn't get it to expand.

(copyable plaintext version)

Sum[Subscript[c, i] x^i, {i, 0, ∞}] //TeXForm


$\sum _{i=0}^{\infty } c_i x^i$

## closed as unclear what you're asking by Daniel Lichtblau, corey979, Coolwater, m_goldberg, MarcoBJul 22 '18 at 3:37

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

Truncate your sum, and use Series:

s = Sum[Subscript[c, i] x^i, {i, 0, 10}];
Series[s^2, {x, 0, 10}] //TeXForm


$c_0^2+2 c_0 c_1 x+\left(c_1^2+2 c_0 c_2\right) x^2+\left(2 c_1 c_2+2 c_0 c_3\right) x^3+\left(c_2^2+2 c_1 c_3+2 c_0 c_4\right) x^4+\left(2 c_2 c_3+2 c_1 c_4+2 c_0 c_5\right) x^5+\left(c_3^2+2 c_2 c_4+2 c_1 c_5+2 c_0 c_6\right) x^6+\left(2 c_3 c_4+2 c_2 c_5+2 c_1 c_6+2 c_0 c_7\right) x^7+\left(c_4^2+2 c_3 c_5+2 c_2 c_6+2 c_1 c_7+2 c_0 c_8\right) x^8+\left(2 c_4 c_5+2 c_3 c_6+2 c_2 c_7+2 c_1 c_8+2 c_0 c_9\right) x^9+\left(c_5^2+2 c_4 c_6+2 c_3 c_7+2 c_2 c_8+2 c_1 c_9+2 c_0 c_{10}\right) x^{10}+O\left(x^{11}\right)$