Solve the equation cos2x - 5cosx = 2

cos2x= 2cos^2x - 1

2cos^2x - 1 - 5cosx = 2

Let cosx = y

2y^2 - 5y - 3 = 0

(2y + 1)(y + 3) = 0

y = -1/2 or -3

cosx = -1/2 or -3

x = 120 degrees

PV
Answered by Pearl V. Maths tutor

12935 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

When do you use Mode, Mean and Median


Find, using calculus, the x coordinate of the turning point of the curve y=e^(3x)*cos(4x) pi/4<x<pi/2 (Edexcel C3)


(19x - 2)/((5 - x)(1 + 6x)) can be expressed as A/(5-x) + B/(1+6x) where A and B are integers. Find A and B


f(x) = (x-5)/(x^2+5x+4), express this in partial fractions and hence find the integral of f(x) dx between x=0 and x=2, giving the answer as a single simplified logarithm.


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