Binomial theorem

The binomial theorem lets you expand any power of a sum:

$(a+b)^n=\sum_{k=0}^{n}\binom{n}{k}a^{\,n-k}b^{\,k}$

where $\binom{n}{k}$ are the binomial coefficients — the next row of Pascal's triangle. For example $(a+b)^4=a^4+4a^3b+6a^2b^2+4ab^3+b^4$.

The calculator gives the full expansion and the list of coefficients. Worth remembering: the sum of all coefficients in a row is $2^n$, and the row is symmetric.