+128 The equation for the circle is:
x2+y2+14x+10y−7=0 .
What is the center of the circle?
+9466 We want to get the equation of the circle into this form:
(x - h)2 + (y - k)2 = r2 , where (h, k) is the center and r is the radius.
x2 + y2 + 14x + 10y - 7 = 0
Subtract 7 from both sides of the equation and rearrange the left side.
x2 + 14x + y2 + 10y = 7
Add (14/2)2 , or 49, and (10/2)2 , or 25, to both sides of the equation.
x2 + 14x + 49 + y2 + 10y + 25 = 7 + 49 + 25
Now we can factor both parts like this
(x + 7)2 + (y + 5)2 = 81
Now that it is in that form, we can see that the center of the circle is (-7 , -5)
+9466 We want to get the equation of the circle into this form:
(x - h)2 + (y - k)2 = r2 , where (h, k) is the center and r is the radius.
x2 + y2 + 14x + 10y - 7 = 0
Subtract 7 from both sides of the equation and rearrange the left side.
x2 + 14x + y2 + 10y = 7
Add (14/2)2 , or 49, and (10/2)2 , or 25, to both sides of the equation.
x2 + 14x + 49 + y2 + 10y + 25 = 7 + 49 + 25
Now we can factor both parts like this
(x + 7)2 + (y + 5)2 = 81
Now that it is in that form, we can see that the center of the circle is (-7 , -5)
+9466 In order to make x2 + 14x a perfect square trinomial, add (14/2)2
x2 + 14x + (14/2)2
x2 + 14x + 72
x2 + 14x + 49
Now it can be factored like this
(x + 7)(x + 7)
(x + 7)2
And whatever you do to one side of the equation, do the same thing to the other side.
So we had to add 49 to both sides. This video might help explain it more:
