Title: Math 310
1Math 310
2Similar Triangles
- Def
- ?ABC is similar to ?DEF, written
?ABC ?DEF, iff ltA is congruent to ltD, ltB is
congruent to ltE, ltC is congruent to ltF and AB/DE
AC/DF BC/EF
3Ex
The two following triangles are similar ?ABC
?DEF.
4AA Property
- Thrm
- If two angles of one triangle are congruent,
respectively, to two angles of a second triangle,
then the triangles are similar. Denoted AA - Note sometimes called the AAA property.
5Ex
Are the two triangles similar? If they are find
the remaining sides.
6Theorem 10-4
- Thrm
- If a line parallel to one side of a triangle
intersects the other sides, then it divides those
sides into proportional segments.
7Ex
8Ex
Suppose line DE is parallel to line segment BA in
triangle ABC. If ratio of BD to DC is 2/3 and CE
is length 3, what is the length of AE?
2
9Theorem 10-5
- Thrm
- If a line divides two sides of a triangle into
proportional segments, then the line is parallel
to the third side.
10Ex
Find the measures of all the interior angles of
triangle ABC.
35, 105 , 40
11Theorem 10-6
- Thrm
- If parallel lines cut off congruent segments on
one transversal, then they cut off congruent
segments on any transversal.
12Ex
Given the three lines are parallel, what is the
length of the segment next to the question mark?
7
13Triangle Midsegment
- Def
- The midsegment of a triangle connects the
midpoints of two adjacent sides of the triangle.
14Midsegment Theorem
- Thrm
- The midsegment is parallel to the third side of
the trianlge and half as long.
15Ex
Given that JI is the midsegment of triangle FGH,
find all the interior angles of the triangle and
the length of the midsegment.
50, 60, 70, 4
16Theorem 10-8
- If a line bisects one side of a triangle and is
parallel to a second side, then it bisects the
third side and therefore is a midsegment.
17Ex
Is the segment JI the midsegment of triangle FGH?
18Indirect Measurement
- One practical use of these theorems is the
ability to measure objects and distances that
would be impossible or impractical to do directly.
19Ex
Book pg 689.