In this exercise is given that a triangle has a vertex R at the coordinate (-4,1) and it is says that this point was rotated 90 degrees counterclockwise from the origin. It is asked to find the rotation which is equivalent to 90 degree counterclockwise rotation.
First of all a 90 degree counterclockwise rotation is define by the rule
(x,y)--(-y,x), which means that every time a 90 degree counterclockwise rotation occurs the given point has to be changed according to the previous mention rule.
In the other hand, a 90 degree clockwise rotation is define by the rule (x,y)--(y,-x). A 360 degree counterclockwise rotation is define by (x,y)--(x,y), and a 270 degree clockwise rotation is represented by the rule (x,y)--(-y,x).
By the previous said, the rotation which is equivalent to a 90 degree counterclockwise rotation is a 270 degree clockwise rotation.
