Mister Exam

Graphing y = arctg(4x-1)

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The graph:

from to

Intersection points:

does show?

Piecewise:

The solution

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f(x) = atan(4*x - 1)
$$f{\left(x \right)} = \operatorname{atan}{\left(4 x - 1 \right)}$$
f = atan(4*x - 1*1)
The graph of the function
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:
$$\operatorname{atan}{\left(4 x - 1 \right)} = 0$$
Solve this equation
The points of intersection with the axis X:

Analytical solution
$$x_{1} = \frac{1}{4}$$
Numerical solution
$$x_{1} = 0.25$$
The points of intersection with the Y axis coordinate
The graph crosses Y axis when x equals 0:
substitute x = 0 to atan(4*x - 1*1).
$$\operatorname{atan}{\left(\left(-1\right) 1 + 4 \cdot 0 \right)}$$
The result:
$$f{\left(0 \right)} = - \frac{\pi}{4}$$
The point:
(0, -pi/4)
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
$$\frac{4}{\left(4 x - 1\right)^{2} + 1} = 0$$
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
$$- \frac{32 \cdot \left(4 x - 1\right)}{\left(\left(4 x - 1\right)^{2} + 1\right)^{2}} = 0$$
Solve this equation
The roots of this equation
$$x_{1} = \frac{1}{4}$$

Сonvexity and concavity intervals:
Let’s find the intervals where the function is convex or concave, for this look at the behaviour of the function at the inflection points:
Concave at the intervals
$$\left(-\infty, \frac{1}{4}\right]$$
Convex at the intervals
$$\left[\frac{1}{4}, \infty\right)$$
Horizontal asymptotes
Let’s find horizontal asymptotes with help of the limits of this function at x->+oo and x->-oo
$$\lim_{x \to -\infty} \operatorname{atan}{\left(4 x - 1 \right)} = - \frac{\pi}{2}$$
Let's take the limit
so,
equation of the horizontal asymptote on the left:
$$y = - \frac{\pi}{2}$$
$$\lim_{x \to \infty} \operatorname{atan}{\left(4 x - 1 \right)} = \frac{\pi}{2}$$
Let's take the limit
so,
equation of the horizontal asymptote on the right:
$$y = \frac{\pi}{2}$$
Inclined asymptotes
Inclined asymptote can be found by calculating the limit of atan(4*x - 1*1), divided by x at x->+oo and x ->-oo
$$\lim_{x \to -\infty}\left(\frac{\operatorname{atan}{\left(4 x - 1 \right)}}{x}\right) = 0$$
Let's take the limit
so,
inclined coincides with the horizontal asymptote on the right
$$\lim_{x \to \infty}\left(\frac{\operatorname{atan}{\left(4 x - 1 \right)}}{x}\right) = 0$$
Let's take the limit
so,
inclined coincides with the horizontal asymptote on the left
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:
$$\operatorname{atan}{\left(4 x - 1 \right)} = - \operatorname{atan}{\left(4 x + 1 \right)}$$
- No
$$\operatorname{atan}{\left(4 x - 1 \right)} = \operatorname{atan}{\left(4 x + 1 \right)}$$
- No
so, the function
not is
neither even, nor odd
The graph
Graphing y = arctg(4x-1)