Question

How do you graph `y=sin(3x)`?

Answer 1

Per. T = `(2pi)/3`
Amp. = `1`

Explanation:

The best thing about sinusoidal functions is that you don't have to plug in random values or make a table. There's only three key parts:

Here's the parent function for a sinusoidal graph:

`color(blue)(f(x)=asin(wx) color(red)((- phi) + k)` Ignore the part in red

First, you need to find the period, which is always `(2pi)/w` for `sin(x), cos(x), csc(x), and sec(x)` functions. That `w` in the formula is always the term next to the `x`. So, let's find our period:

`(2pi)/w = (2pi)/3`. `color(blue)("Per. T" = (2pi)/3)`

Next, we have the amplitude, which is `a`, and generally in front of the trigonometric term, and what the y-coordinates will be every other point. The amplitude can be regarded as the max and min of the graph, as seen above.

So, now we have our amplitude. `color(blue)("Amp."=1)`

When you make a sinusoidal graph, the period will be four x-coordinates to the right and left.

Start with the fourth point, as seen above, which is your period, `color(blue)((2pi)/3)`

Then go to the second point, which is half the period: `color(blue)(((2pi)/3)/2 = pi/3)`

Then go to the first point, which is one fourth the period (or half the second point: `color(blue)((pi/3)/2 = pi/6)`

Now we have our five key points in terms of `color(blue)(pi/6):`

`color(blue)((0,0) (pi/6, 1) (pi/3, 0) (pi/2, -1) ((2pi)/3, 0))`

This is the same as:

`color(blue)((0,0) (pi/6, 1) ((2pi)/6, 0) ((3pi)/6, -1) ((4pi)/6, 0))`

Just notice that the top values are simplified to what the graph shows.

Another important thing to remember is that `Sin(x)` graphs start at the origin and progress upward, unless the amplitude is negative, then they would progress downward. `Cos(x)` graphs start at `(0, "Amplitude")` and move downward, unless the amplitude is negative, then it would start at `(0, "-Amplitude")` and move upward.