You never have to multiply (a + b) by itself over and over. Pascal's triangle hands you the coefficients, and the powers of a and b follow a simple rule. Pick a power, then step through the expansion one term at a time to see exactly where every number comes from.
Every number is the sum of the two directly above it
the row you're using (power n)the term you're on nowthe two “parents” that add to it
Row n holds the coefficients for (a + b)n. Tap any number in the lit row to jump to that term.
Expand a binomialchoose a power and step through it