Hello, yorkey!

I don't think you can "eyeball" the matrix.

You might have to do a teensy bit of math . . .

Let be any vector.

Then: .

It transforms point to the point

Code:Q | * | :* | : * | P : * | * a: * | * : : * | * :b : *| * : ----+------*-----------+---- -b | a |

Point is rotated counterclockwise about the Origin.

. .