A community for students.
Here's the question you clicked on:
 0 viewing
steve816
 one year ago
Please help me solve the inequality!
steve816
 one year ago
Please help me solve the inequality!

This Question is Closed

steve816
 one year ago
Best ResponseYou've already chosen the best response.0I solved for x and got x = 0, 9, 8 Not sure what to do from there.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3so you solved x^3  x^2  72x = 0 for x and you got x = 0, x = 9, x = 8 ??

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3ok first draw a number line and plot those three values on it dw:1440998491371:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3dw:1440998528778:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3label the different regions A,B,C,D dw:1440998552769:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3dw:1440998579792:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3dw:1440998592421:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3dw:1440998604341:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3x^3  x^2  72x factors to x(x9)(x+8) then set up a sign chart where the factors are written in a column on the left side the regions are written along the top row like this dw:1440998659579:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3now let's pick a number from region A this could be any number you want as long as it's less than 8. So let's pick 9 if x = 9, then the sign of x is negative. We put a negative sign/symbol in the first row, first column like this dw:1440998809112:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3keep x = 9 the same what is the value of x9? that is x9 = 99 = 18 which is also negative so place a negative symbol in the "A" column and "x9" row dw:1440998838462:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3if x = 9, then x+8 = 9+8 = 1 which is also negative dw:1440998879510:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3I'm going to let y = x^3  x^2  72x and write "y" in the bottom of the left most column dw:1440998908837:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3to find the sign of y for column A (is y positive or negative?) we multiply the signs in column A negative*negative*negative = positive*negative = negative so ultimately, y is negative when x < 8, ie in region A dw:1440998977212:dw

steve816
 one year ago
Best ResponseYou've already chosen the best response.0So I did all the work and got x < 8 8 < x < 0 x > 9 Is this right?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3does the sign chart make sense? if so, then go ahead and fill out the rest of it so I can see what you got

steve816
 one year ago
Best ResponseYou've already chosen the best response.0I figured out how to use the chart and made sense to me. So I got the answers that I wrote above.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3you should have this sign chart dw:1441000190738:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3take a few moments to check what I got to make sure you got the same things

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3did you get the same table?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3ok great, just checking

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3notice how we want to solve for x in `x^3  x^2  72x > 0` which is the same as `y > 0` since I made `y=x^3  x^2  72x`

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3look in the chart when y > 0 ie when there's a + sign in the y row dw:1441001180490:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3that corresponds to the intervals `8 < x < 0` and `x > 9` dw:1441001210042:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3so the solution to `x^3  x^2  72x > 0` is `8 < x < 0` OR `x > 9` we write \[\Large (8, 0) \cup (9, \infty)\] if we wanted to state the entire solution set in interval notation the graph confirms all this https://www.desmos.com/calculator/6qe6nf0jao

steve816
 one year ago
Best ResponseYou've already chosen the best response.0Wow just wow *clap clap clap* Absolutely brilliant! Thanks for your time and help man, really appreciate it.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.3I'm glad it's all clicking now
Ask your own question
Sign UpFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.