Circle has the equation x2+y2+2x−2y−14=0, how do you graph the circle using the center (h,k) radius r?

1 Answer
Gió
Dec 5, 2015

I found a circle centred at (−1,1) and with radius r=4.

Explanation:

I would write:
(x2+2x)+(y2−2y)=14
add and subtract some values:
(x2+2x+1−1)+(y2−2y+1−1)=14
(x2+2x+1)+(y2−2x+1)−2=14
(x+1)2+(y−1)2=16
or
(x−(−1))2+(y−(1))2=16
(x−(−1))2+(y−(1))2=42
Which is in the form:
(x−h)2+(y−k)2=r2
giving you a circle centred at (−1,1) and with radius r=4.

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