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Differentiating ex ​

The number e is, as we have mentioned before, a very important number. It is important because

y=ex⇒dydx=ex

We sometimes say that ex differentiates to itself.

This means that the gradient of the curve y=ex is equal to ex, as you can see by moving the below point around:

Differentiating ekx ​

We can also differentiate functions of the form

y=ekx

where k is some number.

If

f(x)=ex

then

f(kx)=ekx

is an enlargement in the x direction of scale factor 1k. This makes the gradient steeper by a scale factor of k, as you can see below:

This suggests that

y=ekx⇒dydx=kekx

We're going to assume this is true for now - we'll be able to prove in a couple of chapters' time when we study the chain rule.


Let

f(x)=(ex2−3e−x)ex

and

g(x)=ex+2e3xe5x

Find f′(x) and g′(x)