Proportions and Similar Triangles 8.6
Theorem 8.4 Triangle Proportionality Theorem If a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides proportionally.
Converse of the Triangle Proportionality Theorem If a line divides two sides of a triangle proportionally, then it is parallel to the third side.
Example 1 4 8 12 In the diagram ll , BD=8,DC=4, and AE=12. What is the length of ?
Example 2 Given the diagram, determine whether ll . 21 56 16 48
Find x. 36x = 840 36 36 x = 23⅓
Find x. 2(x + 6) = 5x 2x + 12 = 5x -2x -2x 12 = 3x 3 3 4 = x
Find x. 2.5(8 – x) = 3.5x 20 – 2.5x = 3.5x +2.5x +2.5x 20 = 6x 6 6 6 6 3⅓ = x
Find x. 7 x 3x = 31.5 3 3 3 4.5 x = 10.5
Find x. 6(x + 5) = 10x 6x + 30 = 10x -6x -6x 30 = 4x 4 4 7.5 = x x 6 4 4 7.5 = x
Find x. 12.8x = 115.2 12.8 12.8 x = 9
Find x. 24x = 240 24 24 x = 10 in.
Find x. 12x = 72 12 12 x = 6 ft.
Theorem 8.6 If three parallel lines intersect two transversals, then they divide the transversals proportionally.
Example
Theorem 8.7 If a ray bisects an angle of a triangle, then it divides the opposite side into segments whose lengths are proportional to the lengths of the two sides.
Example 14-x x