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Finding slope of tangetns 
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#1
Apr1408, 06:41 PM

P: 42

Find the slope of the tangent to the parabola y=3x^2 + 4x  7 when x=a. I know how to get the limit using the tangent so i end up with a slope in terms of a (you can also get it using the derivative) but now the next part states:
At what point on the parabola is the tangent perpendicular to the line 3x  4y + 8=0 and all that i get from that question is that the tangent for the point on the parabola will have a slope of 4/3 (negative reciprocal) 


#2
Apr1408, 07:17 PM

P: 588

so you have the derivative in terms of a, right? Let's call it D(a).
You're looking for the value for a such that this expression is equal to 4/3. So what about solving D(a)=4/3 for a ..? 


#3
Apr1408, 07:25 PM

P: 42

sorry... so if the derivative is 6x + 4, then i can say that 6x + 4= 4/3 and solve for a (or x)?



#4
Apr1408, 07:27 PM

P: 588

Finding slope of tangetns
Exactly, sometimes it's easier than you think



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