sin4x = cos2x

How do you solve the equation sin 4x = cos 2x in the interval 0≤x≤180

Thanks

Write the LHS as 2 sin2x cos2x

RichE

Write the LHS as 2 sin2x cos2x

I did that but i ended up only with 2 of the solutions when there were 4 solutions

Draw the graph, and work out the others. That's what I do. Don't forget any negative answers.

ncfcanna

Draw the graph, and work out the others. That's what I do. Don't forget any negative answers.

I still can't get the other two solutions. The solutions i get are 15 and 75

12345678

I did that but i ended up only with 2 of the solutions when there were 4 solutions

So you have to solve cos2x = 0 and sin2x = 1/2

Recall that if x is in the range 0 -> 180 then 2x is in the range 0 -> 360

RichE

So you have to solve cos2x = 0 and sin2x = 1/2

Recall that if x is in the range 0 -> 180 then 2x is in the range 0 -> 360

How did you get to cos2x = 0

12345678

How did you get to cos2x = 0

cos2x - 2sin2xcos2x = 0
cos2x(1-2sin2x) = 0
=> cos2x = 0 or 1 - 2sin2x = 0

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