## anonymous one year ago 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...

1. misty1212

HI!!

2. misty1212

always use radians, they are numbers

3. misty1212

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

4. misty1212

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

5. anonymous

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...

6. anonymous

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?

7. zepdrix

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

8. misty1212

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

9. anonymous

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?

10. misty1212

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

11. zepdrix

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

12. misty1212

yeah it usually does, doesn't it?

13. zepdrix

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

14. zepdrix

Ya I think misty has those backwards :d

15. anonymous

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 ?

16. misty1212

lol totally backwards

17. misty1212

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

18. zepdrix

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

19. anonymous

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