# Thread: equation of semi circle

1. ## equation of semi circle

what is the equation of a semi circle with:

-diameter of 6
-amplitude of 3
-starting at the x-axis
-the center is at (5,0)

and what is the generic equation of a semi circle?
thank you

2. Put your info into the standard equation of a circle

$\frac{(x-5)^2}{9} + \frac{y^2}{9} =1$

and then solve for y and that will give you the equation to a semi circle

$y = \pm \sqrt{9-(x-5)^2}$

3. what is the first formula that you showed? i'm not familiar with it

4. $(x-a)^2 + (y-b)^2 = r^2$

a and being your center points respectively (5,0)

5. oh ok i see it now. sorry, thank you very much though, that helped me out. do you by anychance know how to set restrictions on lines so that it only graphs a segment?

6. Nope but when you find out let me know to please. Still haven't figured out how to do it on my TI89

7. that's exactly what i'm trying to figure out. i'm trying to find the way to set up a domain and range on it and i still can't lol. i'll make sure to tell you if i find something. this is for a project due thursday =p

8. In parametric form, you may let $\cos(t)=\frac{x-5}{3}$ and $\sin(t)=\frac{y}{3}$ to get $\alpha(t)=(x(t),y(t))=(3\cos(t)+5,\sin(t))$ for $t\in[0,\pi]$.