I'm supposed to calculate the differential of f(x)= sin(x)*ln(x)*(x-4)^2 using the product rule. I know what the product rule is but I can't split this into two bits that are easy to differentiate. How do I do it?

You say you are familiar with the product rule i.e. f(x)=u(x)v(x) f'(x)= u(x)v'(x)+v(x)u'(x) (Equation 1)

OK so why don't we try applying that here let's try splitting the function in this problem down into two parts. Let: u(x)=(x-4)^2 v(x)=sin(x)ln(x)

My guess is that v(x) is looking a bit difficult but don't worry we'll get to it. We already have u(x) and v(x) but we need to calculate u'(x) and v'(x). Let's find u'(x):

u(x)=(x-4)^2 u(x)= x^2-8x+16 (multiplied out the brackets) u'(x)=2x-8 (differentiated - multiplied through by the power of x and reduce the power of x by one)

Now we just need v'(x), currently we have:

v(x)=sin(x)*ln(x)

If you look at this, it similar to the problem we had to start with so all we need to do is apply the product rule again. Let: t(x)=sin(x) r(x)=ln(x)

v(x)=t(x)r(x) v'(x)= r'(x)t(x)+t'(x)r(x) (Equation 2)

Try and have a go yourself from here but if you need more help or you've completed the problem and want to check your answer, read on:

We have r(x) and t(x) so let's calculate r'(x) and t'(x):

r(x)= ln(x) r'(x)= x^-1=1/x (recall differential of a log.)

t(x) = sin(x) t'(x) = cos(x) (recall differentials of trig. functions)

Now we can put all the values into Equation 2. We get:

v'(x)= sin(x)/x + cos(x)*ln(x)

Now we've found all the bits for Equation 1 so let's plug in all those values:

f'(x) = (x-4)^2*(sin(x)/x + cos(x)*ln(x))+sin(x)ln(x)(2x-8)

To get comfortable with this, try to solve some other problems that need to be broken down into 3 or more parts in order to be solved.

WH
Answered by William H. Maths tutor

4160 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

What is a radian?


Water is flowing into a rightcircular cone at the rate r (volume of water per unit time). The cone has radius a, altitude b and the vertex or "tip" is pointing downwards. Find the rate at which the surface is rising when the depth of the water is y.


Find the derivative of the following function: f(x) = x(x^3 + 2x)


How do I differentiate y=(4+9x)^5 with respect to x?


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning