Suppose we want the point (x1 y1) to be scaled by a factor sx and by a factor sy along y direction. Then the new coordinates become: x2 = x1 * sx and y2 = y1 * sy
(Note that scaling a point physically means shifting a point away. It does not magnify the point. But when a picture is scaled, each of the points is scaled differently and hence the dimension of the picture changes.)
For example consider a Triangle formed by the points A (5,5), B(10,10) and C (10,5). Suppose we scale it by a factor of 3 along x-axis and 2 along y-axis.
Then the new points will A(5 * 3, 5 * 2)
B(103, 102) and