Proportionality Theorems
Essential Question: What proportion can you write
if a line is parallel to one side of a triangle?
Demonstrated in writing in workbook problems.
Triangle Proportionality Theorem
 If a line is parallel to one side of a
triangle and intersects the other two
sides, then it divides the two sides
proportionally.
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.
Converse of the Triangle
Proportionality Theorem
If a line divides two sides of a triangle
proportionally, then it is parallel to the
third side.
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.
Example: Find 𝑹𝑸.
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.
If three parallel
lines intersect two
transversals then
they divide the
transversals
proportionally.
If a ray bisects an
angle of a triangle,
then it divides the
opposite sides into
segments whose
lengths are
proportional to the
lengths of the other
two sides.
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.
Example: Find the length of 𝐴𝐵
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.
You Try: Workbook Page 118 #1-17 odd
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.
Homework: Page 400 #3-15
multiples of 3
EQ: What proportion can you write if a line is parallel to one side of a triangle?
Demonstrated in writing on workbook problems.