Drawing a circle: y = x^2 + y^2 + 3x + 36 + 4

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MartinSouthey

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Drawing a circle: y = x^2 + y^2 + 3x + 3y + 4

I have a question as part of my assignment, the question involves drawing a circle in graphing software and finding the intercepts against a parabola. Normally this is no issue, however I cant make sense of the equation of the circle. It is given as "Draw the circle y = x^2 +y^2 + 3x + 3y + 4"
rearranging this equation I come to x^2 + 3x + y^2 + 2y = 0. and completing the square gives (x+1.5)^2 + (y + 1)^2 = -0.75. -0.75 cannot be the square of a radius, and hence this equation cannot represent the equation of a circle. Have I done something obviously wrong?
 
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MartinSouthey said:
I have a question as part of my assignment, the question involves drawing a circle in graphing software and finding the intercepts against a parabola. Normally this is no issue, however I cant make sense of the equation of the circle. It is given as "Draw the circle y = x^2 +y^2 + 3x + 3y + 4"
rearranging this equation I come to x^2 + 3x + y^2 + 2y = 0. and completing the square gives (x+1.5)^2 + (y + 1)^2 = -0.75. -0.75 cannot be the square of a radius, and hence this equation cannot represent the equation of a circle. Have I done something obviously wrong?
Click to expand...
My guess is that there's a typo in the circle's equation. Check with your instructor. ;)
 
Yea that was my thought, unfortunately I cant get any help until after the assignment is marked. All i can do is submit an explanation on why i cant solve it. I will keep you posted with the answer when its marked. Cheers
 
Make an assumption as to what might be correct and solve that. Be as clear as you can.
 
MartinSouthey said:
I have a question as part of my assignment, the question involves drawing a circle in graphing software and finding the intercepts against a parabola. Normally this is no issue, however I cant make sense of the equation of the circle. It is given as "Draw the circle y = x^2 +y^2 + 3x + 3y + 4"
rearranging this equation I come to x^2 + 3x + y^2 + 2y = 0. and completing the square gives (x+1.5)^2 + (y + 1)^2 = -0.75. -0.75 cannot be the square of a radius, and hence this equation cannot represent the equation of a circle. Have I done something obviously wrong?
Click to expand...
That does match with heading (Drawing a circle: y = x^2 + y^2 + 3x + 36 + 4) of your post.
 
Bob Brown MSEE said:
xx+yy+3x+3y+4 = 0 is a circle.
could this be the correct equation?
Click to expand...

Yea I thought this is more likely to be the correct equation, however when I plot this against the parabola im given there are no intercepts, which made me start doubting again. I definitely think there is a typo somewhere..
 
Yup, you're correct. Assuming (in the circle's equation) that "y=" is supposed to be "0=" does not lead to an intersection with the parabola.

Could be multiple typos, in the exercise statement.

:idea: You could show initiative, and submit a replacement for the given exercise, by making a second change:

0 = x^2 + y^2 + 3x + 3y - 14 (four intersection points)
 
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