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 May 25th, 2012, 03:31 PM #1 Member   Joined: Jan 2012 Posts: 43 Thanks: 0 Tangent line equation Hey, I'm having trouble with a quotient rule problem that asks you to find the equation of the tangent line. The function is The question then states that when x=9 the corresponding y value will be______ and the slope of the tangent line Is f'(x)=9=_______. Thererore the equation of the tangent line is_______? In form ax+b. For the first blank I just inserted x=9 into the original equation and solved f(x)=-53. For the second blank I got the slope equalling -55/9 by plugging x=9 into the derivative of f(x). I Calculated the Derivative using the product rule And ended up with a derivative of: For the tangent line equation I got By plugging in the coordinates (9,-53) to y+53=(-55/9)x-9 Some part here is incorrect I am not sure which, any help would be much appreciated May 25th, 2012, 03:39 PM #2 Senior Member   Joined: May 2011 Posts: 501 Thanks: 6 Re: Tangent line equation If you plug x=9 into the derivative , you should get . Also, , as you correctly have. So, you now have x=9, y=-53, m=-163/18. All set to find line equation. It may be a little easier to find the derivative by expanding f(x) into Then, term-by-term, we get . Or you can write it as I have above. Just another equivalent form. Is that a picture of you with a TI?. Good to see you're into math. Count yourself as a member of a small minority of the overall population. May 25th, 2012, 03:59 PM #3 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,963 Thanks: 1148 Math Focus: Elementary mathematics and beyond Re: Tangent line equation Though galactus mentioned it (while I was posting ), here is another approach: Now it is a little easier to differentiate. May 25th, 2012, 10:32 PM #4 Member   Joined: Jan 2012 Posts: 43 Thanks: 0 Re: Tangent line equation Ya thanks guys I haven't dealt with product quotient rules in awhile so the different approaches are very helpful as i get back into things. And ya galactus I've always enjoyed math, although the program I'm in is calling for less and less of it as I near the end, unfortunately.. Tags equation, line, tangent Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post math999 Calculus 4 February 25th, 2013 07:36 PM unwisetome3 Calculus 2 October 28th, 2012 06:52 PM unwisetome3 Calculus 4 October 20th, 2012 07:38 AM arron1990 Calculus 5 February 9th, 2012 01:29 AM RMG46 Calculus 28 September 28th, 2011 09:21 AM

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