Hasil bayangan titik M (4,5) akibat rotasi 90° terhadap titik O (0,0) adalah?

M(4,5) —Rot.[O, 90°]— M'(x',y')
• x' = 4.Cos90° - 5.Sin90°
...x' = 4(0) - 5(1)
...x' = -5
• y' = 4.Sin90° + 5.Cos90°
...y' = 4(1) + 5(0)
...y' = 4
maka, koord. titik M'(x',y') = M'(-5,4)