Step by step
The question
Question: solve 2 sin 3x = √2.
Find every angle from 0° up to 360°.
We want the angles from 0° to 360°: one full turn.
1 Name the angle
The angle here is 3x, not x.
We give it a name: u = 3x.
Then the equation is 2 sin u = √2: the kind we can already solve.
2 Find how far u goes
x goes from 0° to 360°.
Times 3 on every part: u = 3x goes 3 times as far, from 0° up to 1080°.
1080° is 3 full turns of the circle.
So u can land on each point 3 times.
3 Remove the 2
2 sin u means 2 times sin u.
We want just sin u.
To remove times 2, we divide by 2.
We do it on both sides, so they stay equal.
2 divided by 2 is 1.
So just sin u is left.
So sin u = √2/2.
4 Find u in the first turn
From the unit circle: sin 45° = √2/2.
So the reference angle is 45°.
Sin is the up value.
The points with that height are on a flat line.
Sin is positive above the x-axis: quadrants I and II.
45° and 180° − 45°: u = 45° or 135°.
On the circle: 2 points.
5 Add full turns
The next turn lands on the same points again: add 360°.
45° + 360° is 405°.
405° + 360° is 765°.
Careful!
Do not stop after one turn!
u goes round 3 times, so every point gives 3 angles.
The same for 135°: 495° and 855°.
6 Divide by 3
u is 3x.
So x is u divided by 3.
45° ÷ 3 is 15°.
135° ÷ 3 is 45°.
And so on.
All are from 0° to 360°.
So x = 15°, 45°, 135°, 165°, 255°, 285°.
7 Check
Let's check every answer.
Put it in, times 3 first, then the unit circle.
Each one must give √2.
Every answer works.
So x = 15°, 45°, 135°, 165°, 255°, 285°.
Let's look back.
First: name the angle.
Then: find how far u goes.
Then: remove the 2.
Then: find u in the first turn.
Then: add full turns.
Then: divide by 3.
Last: check.