Question 98366
C(3,-2). The triangle is rotated 90 degrees counterclockwise. Use the rotation matrix [0 -1][1 0] (please note that [1 0] is directly under [0 -1] but I do not have large enough brackets or the know-how to place it like that)to find the coordinates of C'. 
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[0..-1]
[1...0]

times
[3]
[-2]

C' = 
[2]
[3]
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You can check this out visually by plotting (3,-2),
sketching a circle thru that point with center at 
the origin, then extimate a counter-clockwise 
rotation of 90 degrees.  Do you end up at (2,-3)?
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cheers,
Stan H.