The point P(9, −4) lies on the curve y = 4 / (8 − x).

If Q is the point (x, 4/(8 − x)) find the slope of the secant line PQ (correct to six decimal places) for the following values of x.
a) 9.1 b) 9.001
for a) I keep getting 3.636363 and for b) I keep getting 3.996003. I'm not sure what I'm doing wrong.

4 answers

what makes you think you're wrong?
why do you not show your work?

(f(9..1)-f(9))/(9.1-9) = (-4-(-3.636363))/0.1 = -3.363636
Maybe you just misread your calculator ...
Show your work for the 2nd one
My online homework keeps marking both problems as wrong...
My work for the second one is [(4/(8-9.001) - (-4)]/(9.001 - 9) = [(4/-1.001) - (-4)]/(.001) = (-3.996003996 + 4)/(.001) = (0.003996004)/(.001) = 3.996003
I noticed when you showed your work for the second part, that you
were not consistent in the direction you subtracted .

If your points are,
(9, -4)
(9.001, k)
then you calculate either (k -(-4)) / (9.001 - 9)
or (-4 - k)/(9 - 9.001)

so should have been:

[(4/(8-9.001) - (-4)]/(9.001 - 9) = -3.996003996
= -3.996004 correct to 6 decimals or
[-4 - 4/(8-9.001)]/(9.001 - 9) = -3.996004 correct to 6 decimals

you did - ∆y / ∆x
Thanks so much for your responses. I appreciate it. Part of my error is that I was forgetting to round!
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