Which of the following expresses the possible number of positive real solutions for the polynomial equation shown below?
5x^3+x^2-7x+28=0

Question

Which of the following expresses the possible number of positive real solutions for the polynomial equation shown below?
5x^3+x^2-7x+28=0

anonymous · Answer

attachment

anonymous · Answer

a

cwrw238 · Answer

plz explain how you got that result amysparkly12

cwrw238 · Answer

use Descartes rule of signs

cwrw238 · Answer

@amysparkly12  please explain how you got that result. Refer to this sites Code of Conduct

anonymous · Answer

opps sorry i forgot

cwrw238 · Answer

you count the number of sign changes in the equation  - in this case its 2

cwrw238 · Answer

as its 2 changes there are 0 or 2 positive real solutions

cwrw238 · Answer

to look for real negative solutions you replace x by -x and check for sign changes 

so here we have
-5x^3 +x^2 + 7x + 28 = 0

thats one change of sign so we have 1 or 3 negative real  roots

cwrw238 · Answer

in fact this equation has one negative real root and 2 complex roots

cwrw238 · Answer

its a cubic equation so you'll always have a total of 3 roots

anonymous · Answer

so, it's b

anonymous · Answer

B)three or one?

cwrw238 · Answer

no  the answer is  a for the question which was the number of real positive roots
- I just added the negative root bit for your info.
amysparkly12  was correct

cwrw238 · Answer

Hold on - sorry if I'm confusing you 
- we first found there was 2 or zero positive solutions . That was the first application of Descartes Rule of Signs then we looked for real negatives and found 1 or 3 of these.

cwrw238 · Answer

The question was which of the following expresses the possible number of real positive solutions and the answer to that is A.