Roots of a graph question (I have attached a picture of Q)

Roots of a graph question (I have attached a picture of Q)

Postby Guest » Mon Nov 19, 2018 9:12 am

Please answer the question to the pic attached, thanks. I believe one of the possible values will be K = - 4 but not sure about the other one.
Attachments
IMG-2945.JPG
IMG-2945.JPG (285.25 KiB) Viewed 445 times
Guest
 

Re: Roots of a graph question (I have attached a picture of

Postby HallsofIvy » Tue Mar 05, 2019 11:33 am

I hate having to turn sideways to read a problem. And it probably would have been easier to type the problem in rather than take a picture of the problem and upload it!
The problem is, simply, "The point with coordinates (-4, 0) lies on the graph of y= (x- k)^3- (x- k)^2+ 9(x- k). Find the two possible values of k."
Yes, k= -4 is one of the "possible values of k". But then we have a problem! Setting x= -4, y= 0, in this gives us a cubic equation for k. Clearly k is expected to be real and a cubic equation has either 1 or 3 real roots! And if we allow k to be non-real then there are 3 values. The cannot be "two possible values for k"!

HallsofIvy
 
Posts: 70
Joined: Sat Mar 02, 2019 9:45 am
Reputation: 20

Re: Roots of a graph question (I have attached a picture of

Postby HallsofIvy » Wed Mar 13, 2019 7:04 pm

Looking at this again, -4 is the only real value of k for which (-4, 0) is on that graph. There are NOT "two possible values of k".

HallsofIvy
 
Posts: 70
Joined: Sat Mar 02, 2019 9:45 am
Reputation: 20


Return to Functions, Graphs, Derivatives



Who is online

Users browsing this forum: No registered users and 1 guest