Step by step
The question
Question: solve cos x = 0.
Find every angle from 0° up to 360°.
cos x = 0
We want the angles from 0° to 360°: one full turn.
0° ≤ x < 360°
1 Find every angle
Cos is the across value.
The points with the across value we want are on an up-and-down line.
Cos is 0 straight up and straight down.
x = 90° or 270°.
cos x = 0: x = 90° or 270°
Careful!
The calculator gives only 90°.
But the line crosses the circle twice.
270° works too.
Careful: not only x = 90° ✗
On the circle: 2 points, so 2 angles.
So x = 90°, 270°.
x = 90°, 270°
2 Check
Let's check every answer in the equation.
Each one must give 0.
x = 90°: cos 90° = 0 = 0
x = 270°: cos 270° = 0 = 0
Every answer works.
So x = 90°, 270°.
Let's look back.
First: find every angle.
Last: check.
Answer
x = 90°, 270°