<span>Rules for rotating points about the origin
1. The point (a,b) rotated 90° counterclockwise about
the origin
becomes (-b,a).
</span><span>A′ (-1, 3) B′ (-2, 2) C′ (-2, 1) D′ (-1, 1)
</span>A (a,b)-----------------A′ (-b,a)=(-1, 3)----------->A( 3,1)
B (a,b)-----------------B′ (-b,a)=(-2, 2)----------->B( 2,2)
C (a,b)-----------------C′ (-b,a)=(-2, 1)----------->C( 1,2)
D (a,b)-----------------D′ (-b,a)=(-1, 1)----------->D( 1,1)
