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August 1, 2014

Posted by **demolitrate** on Sunday, February 26, 2012 at 3:03am.

2cos(3x-72)=1

- Maths -
**L.Bianchessi**, Sunday, February 26, 2012 at 3:29amWell I haven't done trig in a long time but u believe...

You divide the 2 to each side to get

Cos(3x-72)=1/2

Then do the inverse to both sides to get rid of the cos and end with 3x-72=60 degrees

So x= 44 degrees

Cosine is positive in quad1&4

So 44degrees and 316degrees.

- Maths -
**L.Bianchessi**, Sunday, February 26, 2012 at 3:47am44&124degrees

- Maths -
**demolitrate**, Sunday, February 26, 2012 at 3:48ambut 3x mean it has turned 360 degree three times, how about the other four ans?

- Maths -
**L.Bianchessi**, Sunday, February 26, 2012 at 4:00amI plugged in 3x-72=___ (set them equal to 420,660,780,1020)

Answer:44,124,164,244,284 degrees

- Maths -
**Reiny**, Sunday, February 26, 2012 at 8:24am2cos(3x-72) = 1

cos(x-7) = 1/2

we know that cos 60° = 1/2 and cos 300° = 1/2

( (inverse)cos .5) = 60 )

3x-72 = 60 or 3x-72=300

3x = 132 or 3x = 372

x = 44° or x = 124° ---> your basic angles

but the period of cos(3x-72) is 360/3 = 120°

so as long as we don't go beyond your given domain, we can add 120° to any previous answer to get a new answer, so

x = 44+120 = 164

x = 164+120 = 284

x = 284+120 = 404 ---> too big

x = 124+120 = 244

x = 244+120364 -- > too big

so x = 44°, 124°, 164°, 244°, and 284°

just like L.Bianchessi found for you in the above post

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