Given that f(x)= (4/x) - 3x + 2 find i) f'(x) and ii) f''(1/2)

This question is asking us to find the first order derivative of f(x) with respect to x, then the second order derivative when x=1/2i) Firstly, let's consider (d/dx)4/x:There are two ways to think about differentiating a fraction like this one. One could use the quotient rule: y=u/v then dy/dx=(v(du/dx) - u(dv/dx))/v^2. However, the simplest method in this case would be to remove the fraction using indices and then use the following differentiation rule: if y=x^2 then dy/dx= 2x.Hence, in this case we would have 4/x = 4x^-1, making f(x)= 4x^-1 - 3x + 2.From here we can use the previously stated differentiation rule to find f'(x). We bring down the -1 and times it by the 4, then take away one from the power: y=4x^-1 then dy/dx = -4x^-2 .We can use the same rule for y=-3x, bring down and multiply the power (in this case 13), then take one from the power (remember anything to the power of 0 equals 1!) : y=-3x then dy/dx= -3Finally, when we differentiate any integer without an x, it differentiates to zero, giving the solution:f'(x)= -4x^-2 - 3ii) To find f''(x) we differentiate by the same method:y=-4x^-2 then dy/dy= (-4-2)x^-3 = 8x^-3Again the integer -3 differentiates to 0, meaning f''(x) = 8x^-3Finally, to find f''(1/2) we need to sub in x = 1/2:f''(1/2) = 8*(1/2)^-3 = 8/(1/2)^3 = 8/(1/8) = (8*8)/1 =64

VB
Answered by Verity B. Maths tutor

5039 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

Find the exact solution to ln(2y+5) = 2 + ln(4-y)


A uniform ladder of mass 5 kg sits upon a smooth wall and atop a rough floor. The floor and wall are perpendicular. Draw a free body diagram for the ladder (you do not need to calculate any forces).


What's the difference between the quotient rule and the product rule?


Prove by induction that the nth triangle number is given by n(n+1)/2


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