I know how to expand binomials with the aid of pascals triangle and also with the aid of the nCr function on the calculator. I'm not quite sure about this formula though see the part in the brackets where n is above k. What does that mean? Someone told me that represents nCk. Is that true? Are you supposed to use that nCr function when using the binomial theorem to expand binomials? I was under the impression that the formula worked out the coefficients without using that nCr function.