Math miscellaneousHard
Question
If f : R → R satisfies f(x + y) = f(x) + f(y), for all x, y ∈ R and f(1) = 7, then 
f(r) is
f(r) isOptions
A.
B.
C.7n (n + 1)
D.
Solution
f(1) = 7
f(1 + 1) = f(1) + f(1)
f(2) = 2 × 7
only f(3) = 3 × 7
f(r) = 7 (1 + 2 + .......+ n)
= 7
.
f(1 + 1) = f(1) + f(1)
f(2) = 2 × 7
only f(3) = 3 × 7
f(r) = 7 (1 + 2 + .......+ n)= 7
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