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onegirl
 3 years ago
2 cos^2 x  3 cos x + 1 = 0 for 0 is less than or equal to x is less than 2pi
onegirl
 3 years ago
2 cos^2 x  3 cos x + 1 = 0 for 0 is less than or equal to x is less than 2pi

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dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1the first term with the cosine... is it: \(\large 2cos^2x \) or \(\large 2cos(2x) \) i'm thinking it's the first one?

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1think of it this way.. let y=cosx so your equation becomes: \(\large 2y^23y+1=0 \) can you solve this quadratic?

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1what is/are the solutions ? y = ???

z3529080
 3 years ago
Best ResponseYou've already chosen the best response.02(2cos^2(x)1)3cosx+1=0 > 4cos^2(x)3cosx1=0 > (4cosx+1)(cosx1)=0

z3529080
 3 years ago
Best ResponseYou've already chosen the best response.0so set 4cosx+1=0 or cos1 =0

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1hmmm.. i got the same but POSITIVE values... i'm double checking...

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1yeah... they should be positive: \(\large 2y^23y+1=0 \) \(\large (2y1)(y1)=0 \) so 2y  1= 0 gives y=1/2 y1 = 0 gives y=1

z3529080
 3 years ago
Best ResponseYou've already chosen the best response.0oh i thought it is cos2x

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1since y=cosx, we have these two equations: \( \large cosx=\frac{1}{2}\) and \(\large cosx=1 \) can you solve these?

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1oops... that second one should be POSITIVE one...

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1do you use the unit circle?

joshi
 3 years ago
Best ResponseYou've already chosen the best response.0this is probably a stupid question, but i'm a bit confused. you said let y = cosx so what happens to the first term 2cos2x? like what about the 2 infront of the x?

onegirl
 3 years ago
Best ResponseYou've already chosen the best response.0@joshi its 2 cos^2 x 3 i made a mistake in typing it

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1ok... so look at what angle gives you a cosine of 1/2.... HINT: there are two of 'em from 0 to 2pi

joshi
 3 years ago
Best ResponseYou've already chosen the best response.0ohhh ok that makes more sense haha

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1yeah... i got a clarification from the asker with my first question... :)

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1dw:1350069794735:dw yep... 60 degrees is one of 'em....

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1you got the second angle?

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1nope... we're still solving cosx = 1/2 , right? x=60 degrees or pi/3 is one... the second solution is in the fourth quadrant...

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1or take a look at page 3: http://tutorial.math.lamar.edu/pdf/Trig_Cheat_Sheet.pdf

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1240 degrees is in the third quadrant... this is the fourth quadrant: dw:1350070347242:dw

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1yes... :) cos(60 degrees) = 1/2 and cos(300 degrees) = 1/2 now solve the other equation: cos x = 1

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1and remember, \(\large 0\color {red}{\le} x<2\pi \)

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1there should be only one solution for this one....

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1using the unit circle, what angle gives you an xcoordinate of 1?

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1yes but 2pi is not included in the interval you're looking at.. 360 degrees = 2pi so what other angle gives you an xcoordinate of 1?

onegirl
 3 years ago
Best ResponseYou've already chosen the best response.0ohhh yea it will 180 degrees

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1no.. cos(180 degrees) = 1 try again....

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1cos x = 1 where \( \large 0\color {red}{\le} x<2\pi\)

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1what about the left side of \(\large 0\color {red}{\le} x<2\pi \) ???? x = 0 ? cos 0 = ???

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1ok... let's put it this way... what's an angle that is coterminal with 360 degrees?

onegirl
 3 years ago
Best ResponseYou've already chosen the best response.0positive 360 and negative 360

dpaInc
 3 years ago
Best ResponseYou've already chosen the best response.1no.. the angle you want is 0 because cos(0 degrees) = 1 so you have 3 solutions: x=0, 60, 300 degrees but since the problem was stated in terms of radians, i'd convert those angles.

onegirl
 3 years ago
Best ResponseYou've already chosen the best response.0so it will be x=1.823 radian
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