For what value of $c$ will the circle with equation $x^2 - 10x + y^2 + 10y + c = 0$ have a radius of length 1?
x^2 - 10x + y^2 + 10y + c = 0 Arange to standard circle form of an equation
x^2 -10x + 25 + y^2 +10y + 25 = -c + 25 + 25
(x-5)^2 + (y+5)^2 = - c +50 circle centered at 5, -5 with radius^2 = - c + 50
if radius = 1 radius^1 = 1 then - c + 50 = 1 c = 49
x^2 - 10x + y^2 + 10y + c = 0 Arange to standard circle form of an equation
x^2 -10x + 25 + y^2 +10y + 25 = -c + 25 + 25
(x-5)^2 + (y+5)^2 = - c +50 circle centered at 5, -5 with radius^2 = - c + 50
if radius = 1 radius^1 = 1 then - c + 50 = 1 c = 49