Question

The graph of function g is a vertical stretch of the graph of function f ​​by a factor of 3.

Answer 1

Question says that the graph of function g is a vertical stretch of the graph of function f ​​by a factor of 3.

Now we have to find about which equation describes function g.

We know that if f(x) is the given function then a*f(x) gives vertical stretch or compress by a factor of a.

when 0<a<1 then it compresses by factor of a.

when a>1 then it stretches vertically by factor of a.

Given that function f is stretched by a factor of a so that means  we use a=3 in formula a*f(x)

Hence final answer will be g(x)=3f(x).

So choice A is correct answer.