General Solution Problem

[Scremin34Egl]

Hi, I need help for this problem,
Determine the general solution for: cos3x-sinx=0

This is what I tried:

cos(2x+x)-sinx=0
cos2x*cosx-sin2x*sinx-sinx=0

Stuck here, I know I have 3 choices for cos2x but dont know what to choose. Please help, thanks.

 

[Deleted member 4993]

Hi, I need help for this problem,
Determine the general solution for: cos3x-sinx=0

This is what I tried:

cos(2x+x)-sinx=0
cos2x*cosx-sin2x*sinx-sinx=0

Stuck here, I know I have 3 choices for cos2x but dont know what to choose. Please help, thanks.

cos(3x) = sin(x)

cos(3x) = cos(π/2 - x)

Can you continue from here.....

 

[Scremin34Egl]

cos(3x) = sin(x)

cos(3x) = cos(π/2 - x)

Can you continue from here.....

I have no idea what you just did, what is that thing divided by 2?, we never did that in school.

 

[Scremin34Egl]

Its okay, I have solved it now, I think you meant 180/2-x ?. Changed Sinx to Cos(90-x) and cancelled the cos and solved,Thanks anyway.

 

[DrPhil]

I have no idea what you just did, what is that thing divided by 2?, we never did that in school.

The "thing" is pi .. just converted sin(x) to a cosine, as you have now done also.