## moongazer 4 years ago Find the radius and the center of the circle. Just check my answer.

1. amistre64

(x-Cx)^2+(y-Cy)^2=r^2

2. moongazer

2x^2 + 2y^2 - 2x + 2y + 7 = 0 My answer is : c(1/2,-1/2) r= $\sqrt{-7/2}$

3. moongazer

Am I right? Cause I am having doubt that my answer is wrong because I have a negative radius

4. amistre64

2x^2 + 2y^2 - 2x + 2y + 7 = 0 2x^2 - 2x + 2y^2 + 2y + 7 = 0 2(x^2 - x) + 2(y^2 +y) = -7 2(x^2 - x +(1/2)^2) + 2(y^2 +y+(1/2)^2) = -7 + 1 2(x-1/2)^2 + 2(y+1/2) = -6 its quite possible that this cannot produce a real circle; just becasue something has some numbers thrown about doesnt make it sensible :) lets chk the wolf

5. amistre64

and make sure that aint spose to be a -7 instead

6. amistre64

http://www.wolframalpha.com/input/?i=2x%5E2+%2B+2y%5E2+-+2x+%2B+2y+%2B+7+%3D+0 as is its right, but no circle

7. mathmate

Check for typos: Could the question be 2x^2 + 2y^2 - 2x + 2y = 7 or 2x^2 + 2y^2 - 2x + 2y - 7 = 0

8. moongazer

That's why I am having doubts with my answer. :) Maybe I just copied the text wrong.

9. moongazer

If it is -7 will the answers be c(1/2,-1/2) r=$\sqrt{7/2}$

10. moongazer

??

11. amistre64

if -7 then we get r^2 = 8 center: (1/2, 1/2)

12. amistre64

-1/2 yeah, but r=sqrt(8) = 2sqrt(2)

13. amistre64

did that wrong somehow, radius is 2 according to the wolf

14. amistre64
15. moongazer

r= (7sqrt(2))/2 ??

16. amistre64

$r^2=7+2(1/2)^2+2(1/2)^2$

17. moongazer

how did it became x = -3/2, x = 5/2 ???

18. amistre64

i see what i did; we divide off the 2 and get 8/2 = 4 sqrt(4) = 2

19. amistre64

your responses arent making sense to me

20. amistre64

$2(x^2 - x +(1/2)^2) + 2(y^2 +y+(1/2)^2) = 7 + 1$ $2(x-(1/2))^2 + 2(y+(1/2))^2 = 8$ $(x-(1/2))^2 + (y+(1/2))^2 = 4$

21. amistre64

those are points on the circle that the wolf handed out

22. moongazer

2(x^2 - x +(1/2)^2) + 2(y^2 +y+(1/2)^2) = 7 + 1 Why did you add one on the right side of the equation?

23. amistre64

becasue we add a total of 1 to the left side 2(1/2)^2 + 2(1/2)^2 = 1

24. amistre64

2x^2 - 2x +2(1/2)^2 + 2y^2 +2y +2(1/2)^2) = 7 + 1 might be easier to see that way

25. amistre64

i dont divide off the "2" right away which might be a difference in our computing techniques

26. moongazer

ohh ok, I forgot adding the numbers that I added on the left side to the right side. That's why I got confused. :) Anyway, I divided the equation directly to "2" but I still got the right answer. :)

27. moongazer

thanks!