# Graphing a vector valued function

• Oct 15th 2011, 06:24 AM
VonNemo19
Graphing a vector valued function
Hi.

I am asked to graph $\vec{r}(t)=2t\vec{i}+\sin(4t)\vec{j}+\cos(4t)\vec{ k}$. How do I go about this?
• Oct 15th 2011, 09:20 AM
emakarov
Re: Graphing a vector valued function
I'll assume that $\vec{i}$, $\vec{j}$ and $\vec{k}$ point along the x-, y- and z-axes, respectively. You see that along the path, $y^2+z^2=\sin^2 4t+\cos^2 4t=1$, so the graph lies on the cylinder with radius 1 going along the x-axis. The x-coordinate grows linearly. If x(t) were constant, then y(t), z(t) would follow a circle. Therefore, this is a spiral. Further, (y(t), z(t)) make 2 revolutions when t ranges from 0 to $\pi$, so when x(t) = 2t, there will be two revolutions when x ranges from 0 to $2\pi$.

• Oct 15th 2011, 09:31 AM
DeMath
Re: Graphing a vector valued function
This is a spiral with the unit radius and the period $\frac{\pi}{2}$, whose center is the x-axis.
See this picture (red: $t=0\ldots\frac{\pi}{2}$, blue: $t=\frac{\pi}{2}\ldots\pi$)

http://www.mathhelpforum.com/math-he...575-spiral.png

For maple

with(plots):
A1 := spacecurve([2*t, sin(4*t), cos(4*t)], t=0..(1/2)*Pi, color=red, thickness=3, numpoints=1000):
A2 := spacecurve([2*t, sin(4*t), cos(4*t)], t=(1/2)*Pi..Pi, color=blue, thickness=3, numpoints=1000):
display(A1, A2, axes=normal);