Enlarging from wrong point
"The Centre Confusion"
The Mistake in Action
Enlarge triangle ABC by scale factor 2, centre O.
Wrong: Each vertex moved 2 squares away from its original position.
Why It Happens
Students apply the scale factor to the shape itself rather than to the distances from the centre of enlargement.
The Fix
For enlargement:
- Draw lines from the centre through each vertex
- Multiply the distance from centre to vertex by the scale factor
- Mark new vertices along these lines
- Join the new vertices
Scale factor 2 means each point is twice as far from the centre as before — not twice as far from where it started.
Key insight: Draw ray lines from the centre through each vertex, then extend.
Spot the Mistake
Can you identify where this student went wrong?
Enlarge by SF 2, centre O
Each vertex moved 2 squares from its original position
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: