From the binomial expansion theorem there are terms in

$\displaystyle x^{k+1}$,$\displaystyle x^ky$, ...... , $\displaystyle xy^k$,$\displaystyle y^{k+1}$.

What are the coefficients of the general term $\displaystyle x^ry^{k+1-r}$ for:

i) r = 0

ii) r = 1,.....,k

iii) r = k + 1