Little confused on this? Just working on parametric equations, I have x= sin theta/2 & y = cos theta/2... and I have to create a plot table between -pie and pie. I don't know if Im supposed to use the radians as the parameter for the plot table or just degrees? i'm confused...

Question

misty1212 · Answer

HI!!

misty1212 · Answer

always use radians, they are numbers

misty1212 · Answer

if it is 
$$x=\sin(\frac{\theta}{2}), y=\cos(\frac{\theta}{2})$$ you should get a circle

misty1212 · Answer

actually because of the $\frac{\theta}{2}$ you get the upper half of a circle

anonymous · Answer

right, I see how it's a circle, i'm just a little confused on the radians, because I'm not understanding what values are supposed to correspond on the table?... I'm sorry if this is confusing, because I'm barely refreshing my trig values and stuff, and I'm not understanding just what values do I use as the parameter...

anonymous · Answer

so would my value -pie correspond to -1? say for like the first value on my table?... if I was just plugging in the value for sin 0/2?

zepdrix · Answer

I guess the start of your interval, $\rm \theta=-\pi$ would correspond to $\rm (x,y)=(-1,0)$
yes?

misty1212 · Answer

here is a nice picture this is what you should get http://www.wolframalpha.com/input/?i=x%3Dsin%28t%2F2%29%2Cy%3Dcos%28t%2F2%29%2C+t+from+-pi+to+pi

anonymous · Answer

ok. great. So If i was plotting the points for the table and I started at -pi, and then -3pi/2, -pi/2, etc. up to pi. Would I just plug in the corresponding degree into the function to be able to graph it by hand.. for example, x= sin theta/2 I would plug in for first value                   sin 1/2 to get my x coordinate?

misty1212 · Answer

at $-\pi$ you get 
$$(\sin(-\frac{\pi}{2}),\cos(-\frac{\pi}{2}))=(0,-1)$$

zepdrix · Answer

Ahh woops :)
I just assumed sine went with the y coordinate haha

misty1212 · Answer

yeah it usually does, doesn't it?

zepdrix · Answer

Oh maybe I didn't...
sin(-pi/2) = -1

zepdrix · Answer

Ya I think misty has those backwards :d

anonymous · Answer

ok. great. I see what your saying, so If I was to plug in the value for -3pi/2 do I just convert that into degrees and make it sin -3pi/2 /2 ?

misty1212 · Answer

lol totally backwards

misty1212 · Answer

i did the cosine first and the sine second, same mistake doe!

zepdrix · Answer

degrees? ew ew ew :(
$$\large\rm \frac{3\pi/2}{2}=\frac{3\pi}{4}$$

anonymous · Answer

oh. ok. I understand now. great. thank you, Yes I was not understanding the x y points. thank you