We know that the slope of a line is given by
Since y is usually the dependent variable and x is usually the independent variable, you may also see
The symbol Δ is the Greek capital letter "Delta" (have button to click to hear delta pronounced), which mathematicians use to mean "change."
We usually use the slope formula to calculate the slope of a line given Δ y and Δ x. If we know the slope and Δ x we can instead use the slope formula to find Δ y.
Using algebra, if
then multiplying both sides by Δ x we get
Therefore if we know the slope of a line and we move over by Δ , then we know y is needs to to change by (slope × Δ x).