Question

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.

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

Thanks so much for your responses. I appreciate it. Part of my error is that I was forgetting to round!