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[apcalculus] Going crazy
Posted:
Oct 10, 2012 4:41 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.  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 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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