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# Do Now - PowerPoint PPT Presentation

Do Now. 1. What are two angles whose sum is 90°? 2. What are two angles whose sum is 180°? 3. A part of a line between two points is called a _________. 4. Two lines that intersect at 90° are ______________ . DWP #60. complementary angles. supplementary angles. segment. perpendicular.

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1. What are two angles whose sum is 90°?

2. What are two angles whose sum is 180°?

3. A part of a line between two points is called a _________.

4. Two lines that intersect at 90° are ______________.

DWP #60

complementary angles

supplementary angles

segment

perpendicular

### 2/26/2014 8-2 B Triangles

Triangle - a closed figure with three line segments and three angles

• Acute triangle-has only acute angles.

• Obtuse triangle- has one obtuse angle.

• Right triangle- has one right angle.

Sara designed this triangular trophy. The measure of E is 38°, and the measure of F is 52°. Classify the triangle.

E

D

F

So the measure of D is 90°. Because DEF has one right angle, the trophy is a right triangle.

P

T

68°

55°

S

R

Example 2

Use the diagram to find the measure of each indicated angle.

QTR

mQTR

= 112°

P

T

m SRT = 180° – (68° + 55°)

68°

55°

S

R

m QRT = 90° – 57°

Example 3

QRT

QRT and SRT are complementary angles, so the sum of mQRTandmSRTis 90°.

= 180° – 123°

= 57°

= 33°

Congruent line segmentshave the same length

Classify the triangle. The sum of the lengths of the sides is 19.5 in.

M

6.5 in.

6.5 in.

L

N

c

If the angles can form a triangle, classify the triangle as acute, obtuse, or right.

1. 37°, 53°, 90° 2. 65°, 110°, 25°

3. 61°, 78°, 41° 4. 115°, 25°, 40°

The lengths of three sides of a triangle are given. Classify the triangle.

5. 12, 16, 25 6. 10, 10, 15

not a triangle

right

acute

obtuse

scalene

isosceles

1. If the following angles can form a triangle, classify the triangle as acute, obtuse, or right.

45, 45, 90

A. acute

B. right

C. obtuse

D. not a triangle

2. If the following angles can form a triangle, classify the triangle as acute, obtuse, or right.

40, 90, 60

A. acute

B. right

C. obtuse

D. not a triangle

3. If the following angles can form a triangle, classify the triangle as acute, obtuse, or right.

26, 85, 69

A. acute

B. right

C. obtuse

D. not a triangle

4. If the following angles can form a triangle, classify the triangle as acute, obtuse, or right.

36, 100, 44

A. acute

B. right

C. obtuse

D. not a triangle

5. The lengths of three sides of a triangle are given. Classify the triangle.

8, 10, 12

A. equilateral

B. isosceles

C. scalene

D. right

The lengths of three sides of a triangle are given. Classify the triangle.

8, 10, 12

6. The lengths of three sides of a triangle are given. Classify the triangle.

12, 8, 12

A. equilateral

B. isosceles

C. scalene

D. right

The lengths of three sides of a triangle are given. Classify the triangle.

8, 10, 12

HOMEWORK Classify the triangle.

• Pg. 461 #1-34 Evens

• Study Ch. 8 Quiz Tomorrow!