All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Just Math > Calculus
When polynomial and trigo unite! (Posted on 2018-04-24) Difficulty: 3 of 5
Find the number of distinct real roots of f(x) = x4 - x3 sin x - x2 cos x.

No Solution Yet Submitted by Danish Ahmed Khan    
No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution solution | Comment 1 of 2
The graph appears to show three real solutions:



The only question might be Does it "wiggle around" near x = 0"? But x^3 and sinx both become negative on the negative-x side and positive on the positive-x side, and x^2 and cos x are also even functions.  The function goes down both to the left and the right of the y-axis and is an even function.

So there are indeed three distinct real roots.

  Posted by Charlie on 2018-04-24 12:52:29
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (0)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2024 by Animus Pactum Consulting. All rights reserved. Privacy Information