If f:R→R satisfies f(x+y)=f(x)+f(y), for all x,y∈R and f(1)=7 ,then ∑nr=1f(r) is

If f:R→R satisfies f(x+y)=f(x)+f(y), for all x,y∈R and f(1)=7 ,the

1.	If f:R→R satisfies f(x+y)=f(x)+f(y), for all x,y∈R and f(1)=7 ,then ∑nr=1f(r) is
Answer» If $f : R \to R$ satisfies $f (x + y) = f (x) + f (y)$ , for all $x, y \in R$ and $f (1) = 7$ ,then $\sum_{r = 1}^{n} f (r)$ is