Equation For a Circle

This lesson shows two examples regarding how to find the equation of a circle centred at the origin. This is one of a series of math video lessons created for the MPM2D grade 10 Academic math course in the province of Ontario, Canada.

Category:

Education

Tags:

• Equation
• For
• Circle
• grade
• 10
• academic
• math
• MPM2D

[nikiannb]

if you're given an equation, say x^2+y^2 = 36, how would you find, from that, one point on the circle? my teacher didn't even bother showing us this..

[AlRichards314]

@nikiannb The radius of this circle is 6 since the square root of 36 is 6. This means that every point on this circle has x coordinates between -6 and 6. So, if you want to find a specific point then replace x with a number between -6 and + 6 and solve for y. For example, if you want to find the point that has an x coordiante of x = 3, then 3^2 + y^2 = 36, 9 + y^2 = 36. Subtracting 9 from both sides we get y^2 = 27, so y = +/- root(27). Then two points on this circle are (3,+/- root(27)).

[StephenYamato]

so, can the equation have a minus sign between the x term and y term?!

[AlRichards314]

@StephenYamato If you change x^2 + y^2 = r^2 into x^2 - y^2 = r^2 it is no longer a circle. The graph becomes a curve called a hyperbola - quite different actually.

[AlRichards314]

Thanks for the comment. I appreciate hearing from people that find my videos useful.

[thabitpulak]

Very nice video sir! I especially liked the way you presented it on your computer in a clear, and interesting way.

If you don't mind, would you tell me what software you used for capturing your desktop movements?

[ZIZERMAN25]

Thanks bro

[asiang00dies]

thanks man! i got a test tommorow and this really helped!

[sebaseba2345]

@gigglepox what kind of teacher do u have ? wow .....

[gigglepox]

thank you man, my teacher forgot to teach us this and I have an exam tomorrow :P

[APMathNerd]

I feel so stupid... I just spent 10 minutes trying to isolate the Y to put it as a function into my calculator... then I remembered the definition of a function... UGGGHHH

[AlRichards314]

@Bakugantsuvai1 Do you mean half root(25), not 52? The radius is root(25), so the diameter is 2Xroot(25).