Help needed

elouisegill

Hello
I'm really struggling with this Q...
sin^2(2x)-cos(2x)-1=0
Any pointers greatly appreciated

Reply 1

mqb2766

Original post by elouisegill

Hello
I'm really struggling with this Q...
sin^2(2x)-cos(2x)-1=0
Any pointers greatly appreciated

Do you know any trig idientities which would make the equation a quadratic in either just cos or just sin?

Reply 2

elouisegill

Original post by mqb2766

Do you know any trig idientities which would make the equation a quadratic in either just cos or just sin?

So I was thinking sin^2(2x)= 1/2(1-cos4x) but not sure :-/

Reply 3

jnsmith

Original post by elouisegill

So I was thinking sin^2(2x)= 1/2(1-cos4x) but not sure :-/

a good idea, but now you have a mixture of cos4x and cos2x, which is not helpful. instead use an identity which keeps everything in terms of cos(2x) or powers

(edited 3 months ago)

Reply 4

davros

Original post by elouisegill

Hello
I'm really struggling with this Q...
sin^2(2x)-cos(2x)-1=0
Any pointers greatly appreciated

Suppose you had

\sin^2{A} - \cos{A} - 1 = 0

. What would you do then?

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