2.7 – Triangles

Type of ∆ Definition Picture

Equilateral Triangle

CL

AS

SIF

ICA

TIO

N B

Y S

IDE

S

All sides are ≅

Type of ∆ Definition Picture

Isosceles Triangle

CL

AS

SIF

ICA

TIO

N B

Y S

IDE

S

2 Sides ≅

base

leg leg

Type of ∆ Definition Picture

Scalene Triangle

CL

AS

SIF

ICA

TIO

N B

Y S

IDE

S

No sides are ≅

Type of ∆ Definition Picture

EquiangularTriangle

CL

AS

SIF

ICA

TIO

N B

Y A

NG

LE

S

All angles are ≅

Type of ∆ Definition Picture

Acute Triangle

CL

AS

SIF

ICA

TIO

N B

Y A

NG

LE

S

All angles are acute

Type of ∆ Definition Picture

Right Triangle

CL

AS

SIF

ICA

TIO

N B

Y A

NG

LE

S

One right angle

leg

leghyp

oten

use

Type of ∆ Definition Picture

Obtuse Triangle

CL

AS

SIF

ICA

TIO

N B

Y A

NG

LE

S

One obtuse angle and 2 acute angles

Classify the triangle by the best definition based on sides and angles. Then find the sum of the interior angles.

scalene

right

180

equilateral

equiangular

180

isosceles

obtuse

180

4. The sum of ANY triangles interior angles is 180°. Use this fact to solve for x below.

x + 75 + 54 = 180

x + 129 = 180

x = 51

2x + 3x + 55 = 180

5x + 55 = 180

x = 25

5x = 125

4x – 1 + 3x + 90 = 180

7x + 89 = 180

x = 13

7x = 91

A = 30 un2

A = ½(12)(5)

A = 30 un2

A = ½(12)(5)

A = 30 un2

A = ½(12)(5)

b

h

b

h

Triangle:

Picture Perimeter Area

Triangle

Add the 3 sides

2

bhA

1

2A bh

30 16 34P 80P in

130 16

2A

2240A in

1

2A bh

20 48 39P 107P cm

148 15

2A

2360A cm

1

2A bh

7 13 10P 30P m

110 5

2A

225A m

1

2A bh

4. If the area of the triangle is 63cm2, find the height of the triangle.

1

2A bh

163 21

2h

126 21h6cm h