don't know how to do this, it said find all the interval form the unit circle.
I try to do: 9sin(2x) =9cos(x)
sin(2x)=9cos(x)/9
sin(2x)=cos(x)
sin(2x)=2(sinx cosx)
then i dont know
please explain...
9 sin(2x) = 9 cos(x)?
2012-01-22 4:29 pm
回答 (2)
2012-01-22 4:37 pm
✔ 最佳答案
So we have:2sinxcosx = cosx
=> 2sinxcosx - cosx = 0
=> cosx(2sinx - 1) = 0
=> cosx = 0....(1) or sinx = 1/2....(2)
so, x = 90° and 270° from (1) and x = 30° and 150° from (2)
:)>
2012-01-23 1:00 am
9sin2x =18sinxcosx ... trig identity sin2x = 2sinxcosx
18sinxcosx = 9cosx ...divide both sides by 9 cos x
2sinx =1
sinx = 1/2
for x between 0 and 360 degrees ( 0 to 2pi radians)
x = 30 degrees = pi/6 radians
x = 150 degrees = 5pi/6 radians
18sinxcosx = 9cosx ...divide both sides by 9 cos x
2sinx =1
sinx = 1/2
for x between 0 and 360 degrees ( 0 to 2pi radians)
x = 30 degrees = pi/6 radians
x = 150 degrees = 5pi/6 radians
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