Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Courses » ap-calculus

Topic: [ap-calculus] larson pg 137 exercise 69
Replies: 1   Last Post: Oct 17, 2012 3:47 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View  
Dosky, Douglas

Posts: 12
Registered: 2/23/09
RE: [ap-calculus] larson pg 137 exercise 69
Posted: Oct 17, 2012 3:47 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

NOTE:
This ap-calculus EDG will be closing in the next few weeks. Please sign up for the new AP Calculus
Teacher Community Forum at https://apcommunity.collegeboard.org/getting-started
and post messages there.
------------------------------------------------------------------------------------------------
Dwayne,

Here is how I solved the problem that you asked.

step 1: we need to find the point that the tangent line and the graph intersect thus we need to set the function equal to the tangent line
5x-4 = x^2 -kx

Step 2: We need to find the derivative so we get f'(x) = 2x - k

Step 3: We know the value of the derivative at the intersection point is 5 so 5 = 2x - k or k = 2x - 5

Step 4: Now lets plug in for k into step 1 so we get
5x - 4= x^2 -x(2x-5)
5x -4 = x^2 -2x^2 + 5x
-4 = -x^2
x = +/- 2

Step 5: Now lets plug in our two x values into step 3 to find our k values
k = 2(-2) - 5 = -9
k = 2(2) - 5 = -1



Take care

Douglas A. Dosky
(c) 614-260-4699
email: ddosky@worthington.k12.oh.us
Thomas Worthington High School
AP Calculus BC and AB Teacher
________________________________________
From: Dwayne Wellington [mrdw27@gmail.com]
Sent: Wednesday, October 17, 2012 9:29 AM
To: AP Calculus
Subject: [ap-calculus] larson pg 137 exercise 69

NOTE:
This ap-calculus EDG will be closing in the next few weeks. Please sign up for the new AP Calculus
Teacher Community Forum at https://apcommunity.collegeboard.org/getting-started
and post messages there.
------------------------------------------------------------------------------------------------
Good morning, I was working on exercise 69 from Larson early Transcendentals and am missing the key to answering the question.


Find the value of k such that the line is tangent to the graph of the function.

(function) f(x) = x^2 - kx (line) y = 5x -4

the answers are x= -1, -9 but I can't seem to get that when I work out the problem. Thank you for the assistance in advance.
---
To search the list archives for previous posts go to
http://lyris.collegeboard.com/read/?forum=ap-calculus

________________________________

***This message and any response to it may constitute public record and thus may be publicly available to anyone who requests it.

Confidentiality Notice: This e-mail message, from Worthington Schools, Worthington, Ohio, including any attachments, is for the sole use of the intended recipient(s) and may contain information that is privileged, confidential and/or exempt from disclosure under applicable law. If you are not the intended recipient or authorized to receive information for the recipient, you are hereby notified that any review, use, disclosure, distribution, copying, printing, or action taken in reliance on the contents of this e-mail is strictly prohibited. If you have received this communication in error, please immediately contact the sender and destroy the material in its entirety. Thank you.

---
To search the list archives for previous posts go to
http://lyris.collegeboard.com/read/?forum=ap-calculus



Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.