Instructions.
Use this interactive board to explore rotations around point \(D\text{:}\)
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Adjust the Angle: Drag the slider at the top left to change the rotation angle. Notice that positive angles rotate the triangle anticlockwise, while negative angles rotate it clockwise.
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Move the Centre: Drag the red point \(D\) to see how changing the centre of rotation affects the final position of the image.
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Observe Congruence: No matter the angle or centre of rotation, notice that the size and shape of the green triangle always exactly match the blue triangle.