geometry
posted by nancy .
In the xy  plane, line l has equation y= x. Point P lies on l and has coordinates (2,2). If l is rotated counterclockwise 45 degrees about the origin, what will be the coordinates of the image of P under this rotation.

Recall your rotation matrix.
(x,y) > (x',y') where
x' = xcosθ  ysinθ
y' = xsinθ + ycosθ
So, plug in your θ.
You can easily check your work by noting that the point will rotate down to the xaxis.
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