Unit 10: Area - Lesson 3

Unit 10: Area

Lesson 3 - Area of Triangles

Vocabulary

Base = the length of the bottom side

Height = How tall the triangle is BUT it must be PERPENDICULAR to the base.

Perpendicular: Two lines cross or touch one another at a 90 degree angle

Multiple Choice

Height of a Triangle must be . . .

• inside the triangle

• parallel to the base

• perpendicular to the base [or touches at a 90 degree angle]

• squared

Multiple Choice

What is the height of this triangle?

• 5 units

• 6 units

• 12 units

• 14 units

Area of a Triangle

 $Area=\frac{1}{2\ }\times base\times height$  

 $Area\ =\ \frac{base\times height}{2}$  
 $A=\frac{1}{2}bh\ \ \ \ or$   $A=\frac{bh}{2}$  

Example

Base = 18
Height = 6

Area = $\frac{1}{2}\times18\times6$  

A =  $\frac{18\times6}{2}$  

Area = 54

Multiple Choice

Find the Area

• 17 units²

• 20 units²

• 10 units²

• 16 units²

Multiple Choice

Find the Area

• 108 cm

• 540 cm

• 108 cm²

• 54 cm²

Multiple Choice

What is the Area of the Triangle in the picture?

• 44.4 mm²

• 5.92 mm²

• 8.88 mm²

• 17.76 mm²

Multiple Choice

Deisel's panda's old habitat was on TRIANGULAR  land in China. Its base was 15 Km long and 26 Km high. What is the area of his panda's habitat? 

• 195 Km²
• 390 Km²
• 400 Km²
• 390 In²

Working Backwords

Often times you will be given the Area of a triangle and one of its measurements, and be required to find the missing measurement.

Step 1: PLUG in to formula

Step 2: isolate the unknown variable by dividing.

Multiple Choice

A triangle has an area of 117 cm². If the base is 26 cm, what is the height?

• 36 cm
• 18 cm
• 9 cm
• 4.5 cm