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sjs2011
Posts:
6
From:
Hagerstown, MD
Registered:
6/28/11


Re: [apcalculus] Going crazy
Posted:
Oct 10, 2012 8:18 PM


NOTE: This apcalculus 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/gettingstarted and post messages there.  Hi Rebecca,
x=.5 is correct. When you differentiate you get 2x and 2x+2, set them equal to get x=.5. So they both have tangents with slope 1 at x=.5. You can then get equations
y.25=x.5 y+4.25=x.5
As far as the x=0 goes, if you look at the graph, y=x^2 has a horizontal tangent at x=0 while the other parabola does not, so this cannot be an option.
Hope this helps!
Joellen Cope Saint James School Hagerstown, MD
On 10/10/12 4:41 PM, "Rebecca Tackett" <rtackett@evansvilledayschool.org> wrote:
>NOTE: >This apcalculus 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/gettingstarted >and post messages there. > > >I need some help with this problem. What am I missing? > > >Graph the two parabolas y=x^2 and y=x^2+2x5 in the same coordinate >plane. Find the equations of the lines that are simultaneously tangent to >both parabolas. I can visualize where the two equations are but now I >can¹t figure out how to write their equations? > >I keep setting the derivatives equal to each other as the slopes of the >same linear equation and solved for x and got x=0 and x=.5, but I don't >think that's correct. And I can't figure out how to write the equation at >either of those points so that it is tangent simultaneously. Any >thoughts? The problem is from Larson 4e, p.201 #2 > >Thanks, >Rebecca Tackett >Upper School Mathematics Instructor >Evansville Day School > > >To search the list archives for previous posts go to >http://lyris.collegeboard.com/read/?forum=apcalculus
 To search the list archives for previous posts go to http://lyris.collegeboard.com/read/?forum=apcalculus



