1.

Let f be a real valued function satisfying `f(x+y)=f(x)+f(y)` for all ` x, y in R and f(1)=2`. Then `sum_(k=1)^(n)f(k)=`A. `(n(n+1))/(2)`B. `n(n+1))`C. `(n+1)`D. `n`

Answer» Correct Answer - B
We have, `f(x)=xf(1)=2x ` for all `x in R `.
`:. Sum_(k=1)^(n)f(k)=sum_(k=1)^(n) 2k=2 sum_(k=1)^(n)k=n(n+1)`


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