The graph of a function $f(x)$ is given. The function consists of a parabolic arc with vertex $V$, a line segment, and a portion of a homographic function. The domain of $f(x)$ is $\mathbb{R}$. We need to find the analytical expression for $f(x)$.

AlgebraPiecewise FunctionsQuadratic FunctionsLinear FunctionsRational FunctionsFunction Analysis
2025/6/29

1. Problem Description

The graph of a function f(x)f(x) is given. The function consists of a parabolic arc with vertex VV, a line segment, and a portion of a homographic function. The domain of f(x)f(x) is R\mathbb{R}. We need to find the analytical expression for f(x)f(x).

2. Solution Steps

Let's analyze the graph and determine the function for each part.
(a) Parabola: The vertex of the parabola is at V=(2,1)V = (-2, 1). The general form of a parabola with vertex (h,k)(h, k) is y=a(xh)2+ky = a(x-h)^2 + k. In our case, h=2h = -2 and k=1k = 1, so y=a(x+2)2+1y = a(x+2)^2 + 1. The parabola is defined for x1x \le -1. When x=1x = -1, we see that y=0y = 0.
So, 0=a(1+2)2+10 = a(-1+2)^2 + 1, which means 0=a(1)2+10 = a(1)^2 + 1, and thus a=1a = -1.
The parabola is f(x)=(x+2)2+1=(x2+4x+4)+1=x24x3f(x) = -(x+2)^2 + 1 = -(x^2 + 4x + 4) + 1 = -x^2 - 4x - 3 for x1x \le -1.
(b) Line Segment: The line segment connects the point (1,0)(-1, 0) to the point (1,1)(1, 1). The equation of a line is y=mx+by = mx + b. We can find the slope m=101(1)=12m = \frac{1-0}{1-(-1)} = \frac{1}{2}. Now we can use the point-slope form yy1=m(xx1)y - y_1 = m(x - x_1) using the point (1,0)(-1,0):
y0=12(x(1))y - 0 = \frac{1}{2}(x - (-1)), so y=12(x+1)=12x+12y = \frac{1}{2}(x + 1) = \frac{1}{2}x + \frac{1}{2}.
This line segment is defined for 1<x1-1 < x \le 1.
(c) Homographic Function: This is a rational function of the form f(x)=ax+bcx+df(x) = \frac{ax+b}{cx+d}. There's a vertical asymptote at x=1x = 1. This means cx+d=0cx + d = 0 when x=1x = 1, so c(1)+d=0c(1) + d = 0, or d=cd = -c. So we have f(x)=ax+bcxcf(x) = \frac{ax+b}{cx-c}. The function passes through (2,4)(2, 4).
4=2a+b2cc=2a+bc4 = \frac{2a+b}{2c-c} = \frac{2a+b}{c}. So 4c=2a+b4c = 2a+b. As xx goes to infinity, the function appears to approach y=2 asymptotically. Thus ac=2\frac{a}{c} = 2, so a=2ca = 2c. Substituting a=2ca = 2c into 4c=2a+b4c = 2a+b gives 4c=2(2c)+b4c = 2(2c) + b, which implies 4c=4c+b4c = 4c + b, so b=0b = 0.
Thus f(x)=2cxcxc=2xx1f(x) = \frac{2cx}{cx-c} = \frac{2x}{x-1} for x>1x > 1.
Combining all the parts, we have:
$f(x) =
\begin{cases}
-x^2 - 4x - 3 & x \le -1 \\
\frac{1}{2}x + \frac{1}{2} & -1 < x \le 1 \\
\frac{2x}{x-1} & x > 1
\end{cases}$

3. Final Answer

$f(x) =
\begin{cases}
-x^2 - 4x - 3 & x \le -1 \\
\frac{1}{2}x + \frac{1}{2} & -1 < x \le 1 \\
\frac{2x}{x-1} & x > 1
\end{cases}$

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