Binomial formula (a+b)^n. Pascal's triangle. Coefficients in binomial formula can be obtained from Pascal's triangle. Every number (except 1) in Pascal's triangle equals sum of two number above. For the numbers from the fifth line 4 = 1 + 3, 6 = 3 + 3, 4 = 3 + 1 and so forth we can write next lines of Pascal's triangle. Similary from binomial formula we can write formulas for power of difference.