Wednesday

July 23, 2014

July 23, 2014

Posted by **kavi** on Friday, November 29, 2013 at 9:55am.

i) using intervals

ii) considering all cases

I did this but my teacher said that when i solved this: x^3-5x^2+2x+8<0

(x+1)(x^2-6x+8)

(x+1)(x-4)(x-2)<0

She told me to show all the steps, but i don't know how to show more. so can you please help me to show all the works and rest of the works i did too but she said " the same answer has to happen for each method. i don't really understand that. can you help me please and thank you....

Steve explained this, but still i didn't got the steps. can someone do it for me step by step so i can understand the steps of it please.

- math ergent please please... -
**Reiny**, Friday, November 29, 2013 at 12:27pmOk, so all the algebra work has been done

x^3-5x^2+2x+8<0

(x+1)(x-4)(x-2)<0

Quickest way:

I would look at the graph of

y = x^3-5x^2+2x+8

= (x+1)(x-4)(x-2)

I know that this is standard cubic function opening up in quadrant I and having x-intercepts of -1, 2, and 4

So a very rough sketch shows me that this curve is below the x-axis ( < 0 ) for x < - 1 or 2 < x < 4

looking at all cases , the critical values of -2,2, and 4 split the line into 4 parts :

if x < -1, try some value, e.g. x = -5

(-)(-)(+) < 0 , so yes

x < -1

if x is between -2 and 2 , e.g. x = 0

(+)(-)(-2) > 0 , so NO

if x is between 2 and 4 , e.g. x = 3

(+)(-)(+) < 0 , so YES

x is between 2 and 4

if x > 4 , e.g. x = 5

(+)(+)(+) > 0 , NO

then x < -2 OR 2 < x < 4

- math ergent please please... -
**Kaplan**, Monday, December 2, 2013 at 1:31pmReiny help me with using intervals. u forgot to help me with that. its urgent please

**Related Questions**

math ergent please... - 10.a)Solve the inequality x^3-5x^2+2x+8<0 by i) using...

math - I am doing something wrong when I work this question. Can someone show me...

Math - Please please help!!!!! Solve the inequality and write the solution set ...

Math[Please Help] - Solve the inequality x > 6x - 10 and write a description ...

inequality - (x-4)/(2x+4) is greater than or equal to 1. How do i express ...

algebra 1 - who is correct and why? chloe jonas 3<2x-5<7 3<2x-5<7 3&...

math - Please solve -2x+7>22 -2x+7-7>22-7 -2x>15 -2x/(-2)<15/(-2) ...

alegbra II - 14. Solve the inquality -3(r-11) + 15 equal or greater than 9. 15....

Math - PLEASE HELP!!!NEED TO SOLVE: 5-(3)<10(-3)= 3<2x+1<9= 13<3x+5&...

Algebra 2(check) cont.. - 1)solve the inequality -3(r-11)+15>_9 my answer = r...