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ktbirdfly


Newbie


Joined: 28 Oct 2009
Posts: 1

Posted: 28 Oct 2009 06:43:31 am    Post subject:

I am having a problem getting the correct graph on a ti84+. It worked fine yesterday but yesterday evening it didn't. The equaiton I am graphing is: y=75+350e^(-.35)(x) and y2=110. Then plot the intersection. When x=6.57 y=110. My calculator says 6-1554.8. Obviously something is set incorrectly but I don't know what it is. The window screen is set to standard -10,10 xmin-max,-10,10 x min-max and all the others items are at one. I am supposed to have a decreasing arc but I am getting a cubic graph and of course the x-y coordinates are incorrect according to my textbook. How do I fix this
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Weregoose
Authentic INTJ


Super Elite (Last Title)


Joined: 25 Nov 2004
Posts: 3976

Posted: 28 Oct 2009 09:50:22 am    Post subject:

Hi, and welcome to United-TI!

For your intersection results, I had to place the x inside the parenthesis of the exponent, which yields:

[font="times new roman"]y1 = y2

75 + 350 e-0.35 x = 110

350 e-0.35 x = 110 − 75

e-0.35 x = (110 − 75) / 350 = 0.1

-0.35 x = ln(0.1)

x = ln(0.1) / -0.35

x = 6.5788145…


Secondly, nothing shows up in the window settings you gave... Using ZoomFit expresses the curve well enough, though: if you select "5:intersect" from the CALC menu and then point your guess down towards the right hand side, it ought to give you the results you expect. In general, when you check to make sure that the problem description is as accurate as the answer you hope to receive, then we'll be able to provide equal help in terms of solving the problem. At any rate, I think this one turned out on the plus side. Smile

Last edited by Guest on 02 Nov 2009 11:30:07 pm; edited 1 time in total
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