The equation x^2+y^2-4x+2y=b describes a circle. Determine the y-coordinate of the center of the circle.
The radius of the circle is 7 units. What is the value of b in the equation?

Question

The equation x^2+y^2-4x+2y=b describes a circle. Determine the y-coordinate of the center of the circle. 
The radius of the circle is 7 units. What is the value of b in the equation?

anonymous · Answer

complete the squares.

anonymous · Answer

$$\left( x^2-4 x+? \right)+\left( y^2+2 y+? \right)=b+?+?$$

anonymous · Answer

$$b+?+?=7^2$$
find b

anonymous · Answer

$$\left( x-h \right)^2+\left( y-k \right)^2=r^2$$
(h,k) is the center and r is the radius.

anonymous · Answer

The equation x^2+y^2-4x+2y=b describes a circle. The radius of the circle is 7 units. What is the value of b in the equation?