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Graphs of points, lines, polynomials, and circles Videos 6 videos
ACT Math: Coordinate Geometry Drill 2, Problem 4. What is the equation for the circle in the video?
ACT Math: Coordinate Geometry Drill 2, Problem 5. What is the origin of the circle?
ACT Math: Coordinate Geometry Drill 3, Problem 3. What is the standard form equation for the line?
ACT Math 2.4 Coordinate Geometry 304 Views
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ACT Math: Coordinate Geometry Drill 2, Problem 4. What is the equation for the circle in the video?
- Coordinate Geometry / Graphs of points, lines, polynomials, and circles
- Product Type / ACT Math
- Foreign Language / Arabic Subtitled
- Foreign Language / Korean Subtitled
- Foreign Language / Spanish Subtitled
- Foreign Language / Chinese Subtitled
- Coordinate Geometry / The relations between equations and graphs
Transcript
- 00:02
Here's your shmoop du jour...
- 00:04
What is the equation for the circle shown?
- 00:06
And here are your potential answers...
- 00:10
If we don't know the formula for a circle, we're basically sunk.
- 00:13
That formula - just to refresh your brain -- is:
Full Transcript
- 00:16
(x -- h)2 + (y -- k)2 = r2 where (h, k)
- 00:22
is the center of the circle and r is the radius.
- 00:25
We just have to figure out the h, k and r. One thing in our court that should make it
- 00:30
easier is that the circle's middle is the origin, or point 0, 0.
- 00:34
We can just plug those in for starters, which gives us the equation:
- 00:38
Quantity x minus 0 squared plus quantity y minus 0 squared equals r squared.
- 00:44
Get rid of the 0's and we have x squared plus y squared equals.....
- 00:49
Well, we know r already because the problem gives us 4 and negative 4 here and here...
- 00:55
so this distance is the radius
- 00:58
The circle's equation has to equal r squared... which is 16.
- 01:02
So the answer is D.
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