Mister Exam
Graphing y = (21-x^2)/(7x+9)
The solution
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2
21 - x
f(x) = -------
7*x + 9
$$f{\left(x \right)} = \frac{21 - x^{2}}{7 x + 9}$$
f = (21 - x^2)/(7*x + 9)
The graph of the function
The domain of the function
The points at which the function is not precisely defined:
$$x_{1} = -1.28571428571429$$
$$x_{1} = -1.28571428571429$$
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:
$$\frac{21 - x^{2}}{7 x + 9} = 0$$
Solve this equation
The points of intersection with the axis X:
Analytical solution
$$x_{1} = - \sqrt{21}$$
$$x_{2} = \sqrt{21}$$
Numerical solution
$$x_{1} = 4.58257569495584$$
$$x_{2} = -4.58257569495584$$
so we need to solve the equation:
$$\frac{21 - x^{2}}{7 x + 9} = 0$$
Solve this equation
The points of intersection with the axis X:
Analytical solution
$$x_{1} = - \sqrt{21}$$
$$x_{2} = \sqrt{21}$$
Numerical solution
$$x_{1} = 4.58257569495584$$
$$x_{2} = -4.58257569495584$$
Extrema of the function
In order to find the extrema, we need to solve the equation
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(the derivative equals zero),
and the roots of this equation are the extrema of this function:
$$\frac{d}{d x} f{\left(x \right)} = $$
the first derivative
$$- \frac{2 x}{7 x + 9} - \frac{7 \left(21 - x^{2}\right)}{\left(7 x + 9\right)^{2}} = 0$$
Solve this equation
Solutions are not found,
function may have no extrema
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(the derivative equals zero),
and the roots of this equation are the extrema of this function:
$$\frac{d}{d x} f{\left(x \right)} = $$
the first derivative
$$- \frac{2 x}{7 x + 9} - \frac{7 \left(21 - x^{2}\right)}{\left(7 x + 9\right)^{2}} = 0$$
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
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
the second derivative
$$\frac{2 \left(\frac{14 x}{7 x + 9} - 1 - \frac{49 \left(x^{2} - 21\right)}{\left(7 x + 9\right)^{2}}\right)}{7 x + 9} = 0$$
Solve this equation
Solutions are not found,
maybe, the function has no inflections
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
the second derivative
$$\frac{2 \left(\frac{14 x}{7 x + 9} - 1 - \frac{49 \left(x^{2} - 21\right)}{\left(7 x + 9\right)^{2}}\right)}{7 x + 9} = 0$$
Solve this equation
Solutions are not found,
maybe, the function has no inflections
Vertical asymptotes
Have:
$$x_{1} = -1.28571428571429$$
$$x_{1} = -1.28571428571429$$
Horizontal asymptotes
Let’s find horizontal asymptotes with help of the limits of this function at x->+oo and x->-oo
$$\lim_{x \to -\infty}\left(\frac{21 - x^{2}}{7 x + 9}\right) = \infty$$
Let's take the limit
so,
horizontal asymptote on the left doesn’t exist
$$\lim_{x \to \infty}\left(\frac{21 - x^{2}}{7 x + 9}\right) = -\infty$$
Let's take the limit
so,
horizontal asymptote on the right doesn’t exist
$$\lim_{x \to -\infty}\left(\frac{21 - x^{2}}{7 x + 9}\right) = \infty$$
Let's take the limit
so,
horizontal asymptote on the left doesn’t exist
$$\lim_{x \to \infty}\left(\frac{21 - x^{2}}{7 x + 9}\right) = -\infty$$
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 (21 - x^2)/(7*x + 9), divided by x at x->+oo and x ->-oo
$$\lim_{x \to -\infty}\left(\frac{21 - x^{2}}{x \left(7 x + 9\right)}\right) = - \frac{1}{7}$$
Let's take the limit
so,
inclined asymptote equation on the left:
$$y = - \frac{x}{7}$$
$$\lim_{x \to \infty}\left(\frac{21 - x^{2}}{x \left(7 x + 9\right)}\right) = - \frac{1}{7}$$
Let's take the limit
so,
inclined asymptote equation on the right:
$$y = - \frac{x}{7}$$
$$\lim_{x \to -\infty}\left(\frac{21 - x^{2}}{x \left(7 x + 9\right)}\right) = - \frac{1}{7}$$
Let's take the limit
so,
inclined asymptote equation on the left:
$$y = - \frac{x}{7}$$
$$\lim_{x \to \infty}\left(\frac{21 - x^{2}}{x \left(7 x + 9\right)}\right) = - \frac{1}{7}$$
Let's take the limit
so,
inclined asymptote equation on the right:
$$y = - \frac{x}{7}$$
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:
$$\frac{21 - x^{2}}{7 x + 9} = \frac{21 - x^{2}}{9 - 7 x}$$
- No
$$\frac{21 - x^{2}}{7 x + 9} = - \frac{21 - x^{2}}{9 - 7 x}$$
- No
so, the function
not is
neither even, nor odd
So, check:
$$\frac{21 - x^{2}}{7 x + 9} = \frac{21 - x^{2}}{9 - 7 x}$$
- No
$$\frac{21 - x^{2}}{7 x + 9} = - \frac{21 - x^{2}}{9 - 7 x}$$
- No
so, the function
not is
neither even, nor odd