Posted by demolitrate on .
solve the following eq. [0<=x<=360]
2cos(3x72)=1

Maths 
L.Bianchessi,
Well I haven't done trig in a long time but u believe...
You divide the 2 to each side to get
Cos(3x72)=1/2
Then do the inverse to both sides to get rid of the cos and end with 3x72=60 degrees
So x= 44 degrees
Cosine is positive in quad1&4
So 44degrees and 316degrees. 
Maths 
L.Bianchessi,
44&124degrees

Maths 
demolitrate,
but 3x mean it has turned 360 degree three times, how about the other four ans?

Maths 
L.Bianchessi,
I plugged in 3x72=___ (set them equal to 420,660,780,1020)
Answer:44,124,164,244,284 degrees 
Maths 
Reiny,
2cos(3x72) = 1
cos(x7) = 1/2
we know that cos 60° = 1/2 and cos 300° = 1/2
( (inverse)cos .5) = 60 )
3x72 = 60 or 3x72=300
3x = 132 or 3x = 372
x = 44° or x = 124° > your basic angles
but the period of cos(3x72) 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