関連ワード:  why is elasticity of demand negative    why is price elasticity of demand negative    why is elasticity of demand always negative    why is income elasticity of demand negative for inferior goods    why is the cross elasticity of demand negative    why is price elasticity of demand always negative    why is price elasticity of demand generally negative    why is coefficient of price elasticity of demand negative    why is the own price elasticity of demand negative    is elasticity of demand negative or positive