Budget constraint line is the combination of two goods which can
be consumed in different quantities by an individual within the
allocated income. With a change in the income level the budget
constriant line itself shifts. The quantity to be consumed within a
budget is for two goods which are labelled on the x and y axis. The
budget constraint line is connecting the two goods combinations
that can be consumed. Relative price changes in any of the goods
changes the consumer preference of consumption. Hence, the slope of
the budget constraint is affected by the relative price of goods
being consumed.