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Topic: [ap-calculus] Going crazy
Replies: 1   Last Post: Oct 10, 2012 4:41 PM

 Rebecca Tackett Posts: 22 Registered: 12/16/10
[ap-calculus] Going crazy
Posted: Oct 10, 2012 4:41 PM

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I need some help with this problem. What am I missing?

Graph the two parabolas y=x^2 and y=-x^2+2x-5 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 can?t 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

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