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Given:

[tex]\[ f(x)=\frac{a}{x+b}+c \][/tex]
[tex]\[ g(x)=2x+5 \][/tex]

- The graph of [tex]\( f \)[/tex] has a vertical asymptote at [tex]\( x=-1 \)[/tex].
- Both graphs intersect the [tex]\( y \)[/tex]-axis at 9.
- The graph of [tex]\( g \)[/tex] intersects the horizontal asymptote of [tex]\( f \)[/tex] at the point [tex]\((-1, y)\)[/tex].

Determine [tex]\( a \)[/tex], [tex]\( b \)[/tex], and [tex]\( c \)[/tex].


Sagot :

To solve for the constants [tex]\( a \)[/tex], [tex]\( b \)[/tex], and [tex]\( c \)[/tex] in the given functions, follow these steps:

1. Identify the vertical asymptote:
[tex]\( f(x) = \frac{a}{x + b} + c \)[/tex]

The vertical asymptote of [tex]\( f(x) \)[/tex] is at [tex]\( x = -1 \)[/tex]. For the function to have a vertical asymptote at [tex]\( x = -1 \)[/tex], the denominator must be zero at this point. Hence:
[tex]\[ x + b = 0 \quad \Rightarrow \quad -1 + b = 0 \quad \Rightarrow \quad b = 1 \][/tex]

2. Y-intercept condition:
Both graphs intersect the y-axis at the same point. This happens when [tex]\( x = 0 \)[/tex]. Therefore:

Evaluate [tex]\( f(0) \)[/tex]:
[tex]\[ f(0) = \frac{a}{0 + b} + c = \frac{a}{1} + c = a + c \][/tex]

Evaluate [tex]\( g(0) \)[/tex]:
[tex]\[ g(0) = 2(0) + 5 = 5 \][/tex]

Since the intersection on the y-axis is at the same point:
[tex]\[ f(0) = g(0) \quad \Rightarrow \quad a + c = 5 \quad \text{(Equation 1)} \][/tex]

3. Intersection point and horizontal asymptote:
The graphs of [tex]\( g \)[/tex] intersects the horizontal asymptote of [tex]\( f \)[/tex]. The horizontal asymptote of [tex]\( f(x) \)[/tex] is the value [tex]\( c \)[/tex], since as [tex]\( x \to \infty \)[/tex], [tex]\( \frac{a}{x + b} \to 0 \)[/tex], hence:
[tex]\[ \lim_{x \to \infty} f(x) = c \][/tex]

We are given that the point of intersection on the y-axis is [tex]\( y = 5 \)[/tex], hence [tex]\( c \)[/tex]:
[tex]\[ y = 5 \quad \Rightarrow \quad c = 5 \][/tex]

4. Solve for [tex]\( a \)[/tex]:
Substitute [tex]\( c = 5 \)[/tex] in Equation 1:
[tex]\[ a + 5 = 5 \quad \Rightarrow \quad a = 0 \][/tex]

Therefore, the values of [tex]\( a \)[/tex], [tex]\( b \)[/tex], and [tex]\( c \)[/tex] are:
[tex]\[ a = 0, \quad b = 1, \quad c = 5 \][/tex]

These are the required constants for the functions based on the given conditions.