The line below has slope . Find the indicated number.
The picture in this case is a little misleading. Since the point whose y-value we want to know is to the left of the point whose y-value we know, Δ x is negative.
Since both the slope and Δ x are negative, their product Δ y is positive:
ynew = yold + Δ y = 7 + 10 = 17.
This makes sense: given the picture, we would expect ynew to be larger than yold.