In Exercises $41-47,$ we define the first difference $\delta f$ of a function $f$ by $\delta f(x)=f(x+1)-f(x)$.
Suppose we can find a function $P$ such that $\delta P(x)=(x+1)^{k}$ and $P(0)=0 .$ Prove that $P(1)=1^{k}, P(2)=1^{k}+2^{k},$ and, more generally, for every whole number $n$
$$P(n)=1^{k}+2^{k}+\cdots+n^{k}$$