Question

If f(x) satisfies f(x+y) = f(x) + f(y) and f(5) = 15 then find f(3)?

• A. 15
• B. 9
• C. 6
• D. 21

Answer 1

The correct option is B

9

We know that if f(x+y) = f(x) + f(y) holds good for a function then function is of f(x) = Kx type.

Let’s assume f(x) = kx , k is a constant

f(5) = 15 [given]

or f(5) = k . 5 = 15

or k = 3

We have to find f(3)

So, f(3) = 3. 3 = 9