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# Help meeeee

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A function $f$ has a horizontal asymptote of $y = -4,$ a vertical asymptote of $x = 3,$ and an $x$-intercept at $(1,0).$ Part (a): Let $f$ be of the form $$f(x) = \frac{ax+b}{x+c}.$$Find an expression for $f(x).$ Part (b): Let $f$ be of the form $$f(x) = \frac{rx+s}{2x+t}.$$Find an expression for $f(x).$

Nov 19, 2019

#1
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If the first function has a horizontal asymptote at  y  =-4

Then the ratio of the coefficients on x in the numerator and denominator is   a / 1  = -4

So a  = -4

If it has an x itercept at (1,0)....then

-4(1) +  b  = 0

-4 + b  = 0

b = 4

And if it has a vertical asymptote at 3.....then

3 + c   =0

c = -3

So   the function is

-4x + 4

f(x)  =    _____

x - 3

Here is a graph :    https://www.desmos.com/calculator/pe4jejs6zo   Nov 19, 2019
#2
+1

The second one uses similar reasoning

r / 2  = -4

r = -8

-8 ( 1)  + s  = 0

-8 + s  = 0

s = 8

2(3) + t  = 0

6 + t  = 0

t = -6

So

-8x  +  8

f(x)  =    ________

2x  -   6

Here is the graph : https://www.desmos.com/calculator/oo1vhoudky   Nov 19, 2019