Use your graphing calculator to find all degree solutions in the interval
0° ≤ x

Question

Use your graphing calculator to find all degree solutions in the interval
0° ≤ x < 360°
for the following equation. (Enter your answers as a comma-separated list.)
cos 3x =
	sqrt2/2
battery on my graphing calculator died, can anyone help?

campbell_st · Answer

well if you have some graphing software just graph 

y = cos(3x)     and y = sqrt2/2 

and find the points where they intersect

this is where the 2 curves are equal.

anonymous · Answer

Don't have any access to anything that can graph atm..

campbell_st · Answer

well you ahve the net, so try wolfram alpha or fooplot

anonymous · Answer

Is it possible to do this without a graphing calculator?

campbell_st · Answer

sure... 

if you use  

$$\cos(3x) = \frac{\sqrt{2}}{2}$$

this is an exact value... 45 degrees

so 

$$3x = \cos^{-1} \frac{\sqrt{2}}{2}$$

or 

3x = 45 

so x = 15 degrees

well to make it easy here is a graph showing points of intersection

hope it helps

campbell_st · Answer

oops sorry, just realised the graph is in radians.... 

so start at 15 and then just keep adding 90 degrees... to the previous...

anonymous · Answer

I've gotten as far as 3x=45, x=15 degrees but I don't think simply adding 90 degrees gets me the answers I need.  If cos 3x=sqrt3/2=10, 110, 130,230,250,350 degrees which doesn't have any patterns such as adding 90 degrees to previous