y = a or f ( x ) = a Graph is a horizontal line passing through the point ( 0,a ) . y = mx + b or f ( x ) = mx + b Graph is a line with point ( 0,b ) and slope m. Graph is a circle with radius ( h , k ) . Graph is an ellipse with center ( h , k ) with vertices a units right/left from the center and vertices b units up/down from the center.