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1. Expand [tex] (1-x)^-^3 [/tex] and express the coefficient of [tex] x^r [/tex] in terms of r.

What i did was to first expand it, according to the binomial series, and I got,

[tex] 1+3x+6x^2........\frac {(-3)(-3-1)....(-3-r+1)}{r!} (-x)^r [/tex]

and the answer is [tex] \frac {(r+1)(r+2)}{2} [/tex]. How do i get from [tex] \frac {(-3)(-3-1)....(-3-r+1)}{r!} [/tex] to the answer? The dots confuse me.