SOLUTION: what does descrates rule of signs tell me about number of real positive zeros and negative real zeros of this function. 5x raised to the 6th-3x raised to the 3rd+x squared-x?

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: what does descrates rule of signs tell me about number of real positive zeros and negative real zeros of this function. 5x raised to the 6th-3x raised to the 3rd+x squared-x?      Log On


   



Question 433594: what does descrates rule of signs tell me about number of real positive zeros and negative real zeros of this function. 5x raised to the 6th-3x raised to the 3rd+x squared-x?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Descartes' rule of signs only gives insight on whether a root is positive or negative, not whether a root is zero.
The polynomial 5x%5E6+-+3x%5E3+%2B+x%5E2+-+x+=+x%285x%5E5+-+3x%5E2+%2B+x%5E1+-+1%29 has a root of 0. Thus apply Descartes' rule only on 5x%5E5+-+3x%5E2+%2B+x%5E1+-+1. Hence, there might 3 positive roots or 1 positive root. (3 variation of signs.)
Considering -5x%5E5+-+3x%5E2+-+x%5E1+-+1, (replacing x by -x), we see that there are no negative roots. (No variation of signs.)
Hence the original polynomial have 0 as a root, 3 positive roots, and 2 complex roots,
OR
have 0 as a root, 1 positive root, and 4 complex roots.