Finding values for a function with horizontal asymptote

**mwok** · November 25th 2008, 12:04 PM

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?

**skeeter** · November 25th 2008, 12:30 PM

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 $b$ .

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