Explain+why+horizontal+and+vertical+lines+have+the+slopes+that+they+have. +One+of+them+has+a+slope+that+is+equal+to+zero,+and+the+other+has+a+slope+that+is+undefined. +What+makes+a+slope+undefined?Set+3

A horizontal line has the slope of zero because in the equation for a horizontal line, m (slope) will always be 0 over something (in a fraction). That makes the slope zero, which makes a flat line. A vertical line has an undefined slope because in its equation, m will always be something over 0, which is not a real number. Therefore, the slope cannot be defined (because it is not a real number).