One-card recap
Dilation from origin: (x, y) → (kx, ky)
k = image/pre-image. k > 1 enlarges. 0 < k < 1 reduces. Similar: matching angles, proportional sides. AA, SAS similarity, SSS similarity. Parallel in a triangle splits proportionally. Altitude to the hypotenuse: three similar right triangles.
Same-number trap still applies: 2 and 1/2 are both on the choice list. Read which figure is the image.