Graph of x sin x
The graph of y = x sin x is a sine wave whose amplitude grows with |x|. It is trapped between the envelope lines y = x and y = −x, touching them whenever sin x = ±1, and crosses zero at every multiple of π.
Key features
- Domain
- All real numbers
- Range
- All real numbers
- Zeros
- x = nπ
- Envelope
- −|x| ≤ y ≤ |x|
- Symmetry
- Even: (−x) sin(−x) = x sin x
- Touches the envelope
- At x = π/2 + nπ, where sin x = ±1
- y-intercept
- None
- Derivative
- sin(x)+xcos(x)
- Antiderivative
- sin(x)−xcos(x)+C
Derivative and antiderivative from the calculator’s algebra system. Domain, range and asymptotes are stated for real x.
What the graph of x sin x looks like
Multiplying sin x by x scales each wave by its distance from the origin. The result is an oscillation that grows linearly, bounded by the lines y = ±x.
Since both x and sin x are odd, their product is even, so the graph is a mirror image across the y-axis. Near the origin it behaves like x², with a minimum at (0, 0).
The peaks are not exactly on the envelope lines: they occur slightly after π/2 + 2nπ, where tan x = −x. The curve touches the envelope at x = π/2 + nπ but crosses through its turning points just beyond.
Points of interest
Found numerically to about twelve digits in the window −15 ≤ x ≤ 15, then shown in exact form where one exists.
- x-intercepts (roots)
- x = −12.5664, x = −9.4248, x = −6.2832, x = −3.1416, x = 0, x = 3.1416 … (9 in view)
- Local maxima
- (−7.9787, 7.9167), (−2.0288, 1.8197), (2.0288, 1.8197), (7.9787, 7.9167)
- Local minima
- (−4.9132, −4.8145), (4.9132, −4.8145)
- Inflection points
- (−12.7223, 1.97574), (−9.62956, −1.95821), (−6.57833, 1.91352), (−3.6436, −1.75324), (−1.07687, 0.948166), (1.07687, 0.948166) … (10 in view)
Table of values
A few points to plot, with exact values where they are simple.
| x | y = x sin x |
|---|---|
| 0 | 0 |
| π/2 | π/2 |
| π | 0 |
| 3π/2 | −3π/2 |
| 2π | 0 |
| 5π/2 | 5π/2 |
| 3π | 0 |
How to graph x sin x by hand
- 1Draw the envelope lines y = x and y = −x lightly.
- 2Mark the zeros at multiples of π.
- 3Draw waves that touch y = x at π/2, 5π/2, … and y = −x at 3π/2, 7π/2, …, crossing zero in between.
- 4Mirror the right half in the y-axis.
Transformations
How the graph moves when you change the formula. The original is x sin x in blue.
y = xThe upper envelope.y = -xThe lower envelope.y = x^2 sin(x)Faster growth, now between ±x².
Frequently asked questions
Is x sin x even or odd?
Where is x sin x zero?
What is the derivative of x sin x?
Related graphs
An odd, growing oscillation between y = ±x.
Period 2π, amplitude 1, zeros at every multiple of π.
A decaying wave with limit 1 at the origin.
The sine wave shifted left by π/2; starts at its peak.
A straight line: slope m, y-intercept b.
The bell curve: peak (0, 1), area √π.
Change the window, add sliders for a, b, h and k, trace the curve with your keyboard, or overlay its derivative.