- #1

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## Homework Statement

2 sin(2x) = 2 cos(x)

## Homework Equations

## The Attempt at a Solution

4sinxcosx-2cosx=0

2(2sinxcosx-cosx)=0

2cosx(sinx-1)=0

2cosx=0 sinx=1

And then I did the math and got pi/2 and 3pi/2 , but that's apparently wrong.

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- Thread starter GuN
- Start date

- #1

- 9

- 0

2 sin(2x) = 2 cos(x)

4sinxcosx-2cosx=0

2(2sinxcosx-cosx)=0

2cosx(sinx-1)=0

2cosx=0 sinx=1

And then I did the math and got pi/2 and 3pi/2 , but that's apparently wrong.

- #2

jedishrfu

Mentor

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- 6,641

I get cosx * (2*sinx - 1) = 0 for your second to last step. Does that help?

- #3

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>_<

I'll try consulting my notes on how to properly calculate cosx=0 and sinx=1/2.

- #4

- #5

- 223

- 10

arccos (0) = x

You have done everything correctly, now you need to figure out what the values for x are. This is not a linear equation, there are 2 series of solutions.

The system I showed you will not be your final answer.

- #6

- 9

- 0

I redid it and got (for the domain of [0, 2pi] ) pi/6, 5pi/6, pi/2 and 3pi/2.

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