When a triangle is rotated by 45 degrees then x1=xcos45-ycos45 and y1=xsin45+ycos45.
While using the equation it is assumed that the rotation is counter-clockwise. A(0,0) is mapped on A1(0,0), B(1,1) is mapped on B1(0,1.4), C(5,2) is mapped on C1(2.1,4.9).
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