Slope is vertical change over horizontal change. Since coordinates conveniently give both the horizontal and vertical coordinates of a points, we can use the coordinates of both points to differentiate, or find the change horizontally and the change vertically between the two points.
4+(−7) is 7 units from 4, in the negative direction (that is, to the left of 4)
This can be solved by using the 30 60 90 triangle. The 30-60 side is equal to 2x, here it is 2x=18. The 60-90 side is equal to x. So this side is 18/2=9. The 30-90 side is by the way equal to the root of x, so here the root of 18