Posted by **Anonymous** on Wednesday, February 22, 2012 at 11:11pm.

sin2x+cosx=0 , [-180,180)

= 2sinxcosx+cosx=0

= cosx(2sinx+1)=0

cosx=0

x1=cos^-1(0)

x1=90

x2=360-90

x2=270

270 doesn't fit in [-180,180) what do I do? Or maybe I did something wrong.

sinx=1/2

x1=sin^-1(1/2)

x1=30

x2=180-30

x2=150

is this correct?

Please and Thank you

- Trig (Last URGENT) -
**Reiny**, Wednesday, February 22, 2012 at 11:18pm
but your domain is from -180 to 180 , so even though 270 will work in the equation , it is beyond your domain.

But, by looking at the cosine graph , you will see that it also has an x-intercept at x = -90°

so for your first one,

x = -90, 0, 90

the second part for sinx = 1/2

your answers of 30° or 150° are correct for the given domain.

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