In the expansion of (x-7)(3x**2+kx-3) the coefficient of x**2 is 0. i) Find the value of k ii) Find the coefficient of x. iii) write the fully expanded equation in terms of x

i) multiply out: 3x3+kx2-3x-21x2-7kx+21 simplify: 3x3+(k-21)x2+(-7k-3)x+21 the coefficient of x2 is 0 and therefore k-21=0 k=21.
ii)from i) the coefficient of x is (-7k-3) k=21 and therefore the required answer is (-7*21)-3 =-147-3 =-150 iii) from i) and ii): 3x3+(k-21)x2+(-7k-3)x+21 -> 3x**3-150x+21

Answered by Further Mathematics tutor

2218 Views

See similar Further Mathematics GCSE tutors

Related Further Mathematics GCSE answers

All answers ▸

Use the factor theorem to show that (x-1) is a factor of x^3 - 3x^2 -13x + 15


If the equation of a curve is x^2 + 9x + 8 = y, then differentiate it.


Given a^2 < 4 and a+2b = 8. Work out the range of possible values of b. Give your answer as an inequality.


f(x) = 2x^3+6x^2-18x+1. For which values of x is f(x) an increasing function?


We're here to help

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

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences