Given: 𝑓(π‘₯) = π‘Žπ‘₯^3 + 𝑏π‘₯^2 βˆ’ 3 and 𝑓"(βˆ’2) = 0. If it is further given that the point (βˆ’3; 6) lies on the graph of 𝑓. Show that π‘Ž = 1/3 and 𝑏 = 2.

We start off by finding the first derivative of equation f(x) = ax3 + bx2 - 3: f'(x) = 3ax2 + 2bx. We now take the second derivative of equation f, because we have been told that f"(-2) = 0: f"(x) = 6ax + 2b (1). We know that with an x value of -2, equation (1) is equal to 0: f"(-2) = 6a(-2) + 2b = 0-12a +2b = 0 (2). This equation will be used later to find the final answer. We also know that the pointΒ (βˆ’3; 6) lies on the graph of 𝑓. Therefore, for an x value of -3, f(x) equals 6: f(-3) = a(-3)2 + b(-3)2 - 3 = 6-27a + 9b = 9 (3). We then solve equations (2) and (3) simultaneously, as we have two unknowns and two equations, and reach the following answer: a = 1/3 ; b = 2. This question would be worth a total of 6 points.

Answered by Neil L. β€’ Maths tutor

2076 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers β–Έ

There are only red , blue and purple counters in a bag. The ratio of the number of red counters to the number of blue counters is 3 : 17. If a counter is taken randomly the probability that it is purple is 0.2 Work out the probability for it to be red.


Finding the length of the side opposite a known angle while having the hypotenuse length known


Find the value of X when 3x^2 + 6x + 3 = 0


Simplify fully 3/(2x + 12) - (x - 15)/(x^2 - 2x - 48)


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

Β© MyTutorWeb Ltd 2013–2024

Terms & Conditions|Privacy Policy
Cookie Preferences