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Plotting a function graph/ (x^2-9)/(x+3)

Graphing y = (x^2-9)/(x+3)

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The graph:

from to

Intersection points:

does show?

Piecewise:

The solution

You have entered [src] 
        2    
       x  - 9
f(x) = ------
       x + 3
f(x)=x2−9x+3f{\left(x \right)} = \frac{x^{2} - 9}{x + 3} 
f = (x^2 - 9)/(x + 3)
The graph of the function
02468-8-6-4-2-1010-2020
The domain of the function
The points at which the function is not precisely defined:
x1=−3x_{1} = -3
The points of intersection with the X-axis coordinate
Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
x2−9x+3=0\frac{x^{2} - 9}{x + 3} = 0
Solve this equation
The points of intersection with the axis X:

Analytical solution
x1=3x_{1} = 3
Numerical solution
x1=3x_{1} = 3
The points of intersection with the Y axis coordinate
The graph crosses Y axis when x equals 0:
substitute x = 0 to (x^2 - 9)/(x + 3).
−9+023\frac{-9 + 0^{2}}{3}
The result:
f(0)=−3f{\left(0 \right)} = -3
The point:
(0, -3)
Extrema of the function
In order to find the extrema, we need to solve the equation
ddxf(x)=0\frac{d}{d x} f{\left(x \right)} = 0
(the derivative equals zero),
and the roots of this equation are the extrema of this function:
ddxf(x)=\frac{d}{d x} f{\left(x \right)} =
the first derivative
2xx+3−x2−9(x+3)2=0\frac{2 x}{x + 3} - \frac{x^{2} - 9}{\left(x + 3\right)^{2}} = 0
Solve this equation
Solutions are not found,
function may have no extrema
Inflection points
Let's find the inflection points, we'll need to solve the equation for this
d2dx2f(x)=0\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
d2dx2f(x)=\frac{d^{2}}{d x^{2}} f{\left(x \right)} =
the second derivative
2(−2xx+3+1+x2−9(x+3)2)x+3=0\frac{2 \left(- \frac{2 x}{x + 3} + 1 + \frac{x^{2} - 9}{\left(x + 3\right)^{2}}\right)}{x + 3} = 0
Solve this equation
Solutions are not found,
maybe, the function has no inflections
Vertical asymptotes
Have:
x1=−3x_{1} = -3
Horizontal asymptotes
Let’s find horizontal asymptotes with help of the limits of this function at x->+oo and x->-oo
lim⁡x→−∞(x2−9x+3)=−∞\lim_{x \to -\infty}\left(\frac{x^{2} - 9}{x + 3}\right) = -\infty
Let's take the limit
so,
horizontal asymptote on the left doesn’t exist
lim⁡x→∞(x2−9x+3)=∞\lim_{x \to \infty}\left(\frac{x^{2} - 9}{x + 3}\right) = \infty
Let's take the limit
so,
horizontal asymptote on the right doesn’t exist
Inclined asymptotes
Inclined asymptote can be found by calculating the limit of (x^2 - 9)/(x + 3), divided by x at x->+oo and x ->-oo
lim⁡x→−∞(x2−9x(x+3))=1\lim_{x \to -\infty}\left(\frac{x^{2} - 9}{x \left(x + 3\right)}\right) = 1
Let's take the limit
so,
inclined asymptote equation on the left:
y=xy = x
lim⁡x→∞(x2−9x(x+3))=1\lim_{x \to \infty}\left(\frac{x^{2} - 9}{x \left(x + 3\right)}\right) = 1
Let's take the limit
so,
inclined asymptote equation on the right:
y=xy = x
Even and odd functions
Let's check, whether the function even or odd by using relations f = f(-x) и f = -f(-x).
So, check:
x2−9x+3=x2−93−x\frac{x^{2} - 9}{x + 3} = \frac{x^{2} - 9}{3 - x}
- No
x2−9x+3=−x2−93−x\frac{x^{2} - 9}{x + 3} = - \frac{x^{2} - 9}{3 - x}
- No
so, the function
not is
neither even, nor odd
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