Pre-Algebra: Chapter 11-6
Similar Triangles
If 2 triangles are similar, then the corresponding angles are congruent. If 2 triangles are similar, them their corresponding sides are proportional. Similar triangles have the SAME SHAPE but not necessarily the SAME SIZE are similar figures. You can use proportions to find the measures of the sides of similar triangles when some measures are known.
Algebra: Chapter 13-3
Solving quadratics by completing the squares
Purplemath explains it better than I can in this blog, just click here for step-by-step instructions.