Suppose that f(x)=∞∑n=0anxn and that g(x)=∞∑n=0bnxn. Then we can get the power series for f(x)+g(x), f(x)g(x) and f(x)/g(x) by adding, multiplying, and dividing these expressions, as if they were polynomials:
f(x)+g(x)=∞∑n=0(an+bn)xn.
f(x)g(x)=∞∑n=0cnxn, where cn=n∑i=0aibn−i.
Computing f(x)/g(x), however, is trickier as we have to perform long division, and treat larger powers of x as being less important than smaller powers.