Formula used:

where,

Let,

Here, f(x) = e^x

Now, by putting x = a in f(x) we get,

f(a) = e^a

f(a + h)

= (e)^a+h

= e^a+h

Similarly, f(a + 2h)

= e^a+2h

Sum of n terms of a G.P. is given by,

Therefore,