Find all angles between 0 and 2pi satisfying the condition cosx=-1/2

You can find the angles using the unit circle. You can also find the angle using algebra.

I want to show you the algebra way.

Since cos(x) = cos(2•pi - x), this leads to two equations.

The two equations are as follows:

cos (x) = -1/2...the given problem.

We also have cos (2•pi - x) = -1/2.

To isolate x for both trigonometric equations, use the inverse trig function idea.

Equation 1

arccos(cos x) = arccos (-1/2)

x = 2•pi/3

Equation 2

arccos(cos (2•pi - x)) = arccos (-1/2).

Note: 2•pi - x = 2•pi/3. We are not done with this equation. We must isolate x. In other words, like any other equation, solving for x is needed.

When we subtract 2•pi from both sides, the answer for x in the second equation is 4•pi/3.

As you know, 2•pi/3 and 4•pi/3 lie between 0 and 2•pi on the unit circle.

2•pi/3, 4•pi/3

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step-by-step explanation: