# Finding values for a function with horizontal asymptote

• November 25th 2008, 12:04 PM
mwok
Finding values for a function with horizontal asymptote
Find values of a,b, and c for exponential function f(x) = cb^-x + a. Given that horizontal asymptote is y=72. Y-intercept is 425 and point P(1,248.5) lies on the graph.

Can anyone explain this step-by-step?
• November 25th 2008, 12:30 PM
skeeter
Quote:

Originally Posted by mwok
Find values of a,b, and c for exponential function f(x) = cb^-x + a. Given that horizontal asymptote is y=72. Y-intercept is 425 and point P(1,248.5) lies on the graph.

Can anyone explain this step-by-step?

as x gets large, $cb^{-x}$ gets very small ... $a = 72$

y-intercept at $x = 0$ ... $cb^0 + 72 = 425$ ... $c = 353$

$x = 1$ ... $248.5 = 353 \cdot b^{-1} + 72$

you solve for $b$.