Find an equation of the circle that satisfies the given conditions.
Center (−4, 7); passes through (−9, −8)

Question

Find an equation of the circle that satisfies the given conditions.
Center (−4, 7);    passes through (−9, −8)

whpalmer4 · Answer

Formula for a circle with radius $r$ and center $(h,k)$ is $$(x-h)^2 + (y-k)^2 = r^2$$

Formula for the distance between two points $(x_1,y_1)$ and $(x_2,y_2)$ is $$d = \sqrt{(x_2-x_1)^2 + (y_2-y_1)^2}$$

Use the second formula to find the radius, which is simply the distance between the center and a point through which the circle passes.  With the radius in hand, fill in the blanks in the formula for the circle and you're done.

whpalmer4 · Answer

Because the circle formula asks for $r^2$, you don't have to even both with the square root in the distance formula: $r^2 = (x_2-x_1)^2 + (y_2-y_1)^2$

anonymous · Answer

Show that the equation represents a circle by rewriting it in standard form.
4x2 + 4y2 + 8x − y = 0

whpalmer4 · Answer

Complete the square on x and y to achieve that.

anonymous · Answer

but how when it equals zero? i get that i would have to divide everything by 4 but then i will never have a radius