variation

is a function defined by an equation where k is the constant of variation, and k is not equal to 0

y varies directly as x

y varies as x

y is directly proportional to x

y is proportional to x

when x increases (decreases), y also increases (decreases)

the graph shows straight a straight line

is a function which shows that two quantities vary inversely, that is, their product is a constant

y inversely as x

x increases, y decreases