Download 6-1 Proportions Ratio—a comparison of two quantities Proportion

6-1 Proportions
Ratio—a comparison of two quantities
Proportion—an equation of the form a/b = c/d that states that two ratios are equal
Cross products—in the proportion a/b = c/d where b does not equal 0 and d does not equal 0, the
cross products are ad and bc. The proportion is true if and only if the cross products are equal.
Extremes—in a/b = c/d, the numbers a and d.
Means—in a/b = c/d, the numbers b and c.
6-2 Similar Polygons
Similar polygons—two polygons are similar if and only if their corresponding angles are
congruent and the measures of their corresponding sides are proportional.
Scale factor—the ratio of the lengths of two corresponding sides of two similar polygons or two
similar solids.
6-3 Similar Triangles
Postulate 6.1
Angle-Angle (AA) Similarity
If the two angles of one triangle are congruent to two angles of another triangle, then the
triangles are similar.
Theorems
6.1 Side-Side-Side (SSS) Similarity
If the measures of the corresponding sides of two triangles are proportional, then the triangles are
similar.
6.2 Side-Angle-Side (SAS) Similarity
If the measure of two sides of a triangle are proportional to the measures of two corresponding
sides of another triangle and the included angles are congruent, then the triangles are similar.
6.3 Similarity of triangles is reflexive, symmetry, and transitive.
6.4 Parallel Lines and Proportional Parts
Theorem 6.4
Triangle Proportionality Theorem
If a line is parallel to one side of a triangle and intersects the other two sides in two distinct
points, then it separates these sides into segments of proportional lengths.
Theorem 6.5
Converse of the Triangle Proportionality Theorem
If a line intersects two sides of a triangle and separates the sides into corresponding segments of
proportional lengths, then the line is parallel to the third side.
Theorem 6.6
Triangle Midsegment Theorem
A midsegment of a triangle is parallel to one side of the triangle, and its length is one-half the
length of that side.
Corollaries
6.1 If three or more parallel lines intersect two transversals, then they cut off the transversals
proportionally.
Corollaries
6.2 If three or more parallel lines cut off congruent segments on one transversal, then they cut off
congruent segments on every transversal.
6.5 Parts of Similar Triangles
Theorem 6.7
Proportional Perimeters Theorem
If two triangles are similar, then the perimeters are proportional to the measures of corresponding
sides.
Theorem 6.8
If two triangles are similar, then the measures of the corresponding altitudes are proportional to
the measures of the corresponding sides.
Theorem 6.9
If two triangles are similar, then the measures of the corresponding angle bisectors of the
triangles are proportional to the measures of the corresponding sides.
Theorem 6.10
If two triangles are similar, then the measures of the corresponding medians are proportional to
the measures of the corresponding sides.
Theorem 6.11
Angle Bisector Theorem
An angle bisector in a triangle separates the opposite side into segments that have the same ratio
as the other two sides.
6-6 Fractals and Self-Similarity
Iteration—a process of repeating the same procedure over and over again
Fractal—a figure generated by repeating a special sequence of steps infinitely often. Fractals
often exhibit self-similarity
Self-similar—if any parts of a fractal image are replicas of the entire image, the image is selfsimilar