Parts of Similar Triangles

When two triangles are similar, ALL corresponding linear measurements are in the same ratio (the scale factor).

Proportional Parts

• Corresponding sides are proportional.
• Corresponding altitudes are proportional.
• Corresponding medians are proportional.
• Corresponding Angle bisectors are proportional.
• Corresponding perimeters are proportional.

Angle Bisector / Side Proportion

An Angle bisector of a Triangle divides the opposite side in the ratio of the two adjacent sides:

If BD bisects ∠B in △ABC, then AD/DC = AB/BC.

All these linear ratios equal the scale factor k. Areas are in the ratio k².