Assuming that the consumer consumes only two goods X and Y and is in equilibrium. Then , `(MU_(x))/(P_(x))=(MU_(y))/(P_(y))`
Now suppose Px falls ,then `(MU_(x))/(P_(x))gt(MU_(y))/(P_(y))`
Since per rupee marginal utility of X is greater than per rupee marfinal utility of Y , the consumer will buy more of X . It shows inverse relation between price of X and demand for X.
