Geometry help on inverse transformation?

Question

i need help on my homework;

what is the inverse of Rotation x? (Rx)

what is the inverse of Half turn o? (Ho)

what is the inverse of Rotation o, 90 degrees? (Ro, 90)

Answer 1

The inverse is what undoes it.  What undoes a rotation by 90 degrees?  A rotation in the opposite direction, also by 90 degrees.  What undoes a half-turn?  Well, obviously turning it a half-turn in the opposite direction.  You might also notice that another half-turn in the same direction will do the same thing, so it is its own inverse.  What's the inverse of rotation x?  Rotation in the opposite direction by x.  Since the notation is non-standard, I can't tell you how to write those down symbolically.  For a rotation of x in the opposite direction, the most obvious possibilities are -Rx and R(-x).  You'll have to check your text or your notes to know which, if either, is right.