For what value of k does the equation x^2+10x+y^2+16y-k=0 represent a circle of radius 6?
+36916 x^2+10x+y^2+16y = k now complete the square for x and y
(x+5)^2 + ( y+8)^2 = 25 + 64 +k the red part = r^2 ( which = 6^2 = 36)
r^2 = 89 + k = 36 solve for k
k = -53
