Find the differential of the function

a. y=x4sin(9x)
b. y=x4sin⁡(9x).

We want to find:

Where:

Remember that when we have a function like:

f(x) = g(x)*h(x)

The derivation gives:

f'(x) = g'(x)*h(x) + g(x)*h'(x)

In this case we can define:

f(x) = y

g(x) = x^4

h(x) = sin(9x)

These functions are easy to differentiate:

g'(x) = 4*x^3

h'(x) = 9*cos(9*x)

Then we have:

Then we can write: