Enlargement scales the shape from a centre point by a scale factor k.
- ∣k∣>1: image is bigger.
- ∣k∣<1: image is smaller.
- k>0: same side of centre.
- k<0: OPPOSITE side of centre.
About the origin. Multiply each coordinate by k.
Worked example. Enlarge (4,2) by scale factor 2 from origin: (8,4).
Worked example. Enlarge (4,2) by scale factor −2 from origin. Multiply by −2: (−8,−4). Note image is in the OPPOSITE quadrant.
Worked example. Enlarge (4,2) by scale factor 21 from origin: (2,1). Image is HALF the size.
About a non-origin centre (cx,cy).
x′=cx+k(x−cx),y′=cy+k(y−cy)
I.e., translate centre to origin, scale, translate back.
Describing. "Enlargement, scale factor −2, centre (0,0)." State BOTH scale factor AND centre.
Edexcel tip. Negative scale factor catches many students. The image is ROTATED 180° AS WELL as scaled — it's NOT just on a different side; it's flipped.