Square trig graphs

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We had a test recently in trig on graphing trig functions. I found it all quite simple except a problem that we had not discussed. I believe the problem was something like y=cos^2(x). I graphed it by squaring each cosine value, because i had no idea what else to do, but when i turned the test in, my teacher told me that it was only half correct. I ended up with a nice M (maybe W) shape. Thinking back, would it have been correct to change the equation to y=(1+cos2x)/2 and then graph it?
 

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symbolipoint
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tycon69, what are you trying to express? Are you asking about [cos(x)]*[cos(x)], or what? You seem to mean just that. All the values will be positive (the 'y' values). The 'M' shape that your teacher indicated. The amplitude is 1.
 
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Maybe you took the squares of negative cosines as negative? cos^2(x) is greater than 0 everywhere, was your graph?
 
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yes it was, it's amplitude was one and everything was above 0. I just graphed it on a graphing application and the graph is identical to what i graphed. I must have overlooked a simple mistake, i'll have to look at it monday. Luckily she only counted off half so i ended up with an A. Thx for trying to help me, i know my explanation was quite confusing.
 
HallsofIvy
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We had a test recently in trig on graphing trig functions. I found it all quite simple except a problem that we had not discussed. I believe the problem was something like y=cos^2(x). I graphed it by squaring each cosine value, because i had no idea what else to do, but when i turned the test in, my teacher told me that it was only half correct. I ended up with a nice M (maybe W) shape. Thinking back, would it have been correct to change the equation to y=(1+cos2x)/2 and then graph it?
What was the problem? Just to graph the function?
 
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Yes, the problem was just to graph the function. I found out it was a pretty stupid mistake on my part in that i graphed cos(0)=0 when it should have of course been 1:bugeye:
 

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