Area of a triangle and trapezoid

Area of a triangle and trapezoid

write down the formulas

Notice anything about the triangles?

Triangles are just rectangles cut in half

Area of a triangle

* multiply the base x height and then divide by 2

Triangle Example

 $A\ =\ \frac{6\ \times\ 18}{2}$  

 $A\ =\ \frac{108}{2}=\ 54$  

Multiple Choice

What is the area?

• 12 cm²
• 14
• 14 cm²
• 24 cm²

Find the missing side

1. take the area and multiply it by 2

2. divide by the other side

Solve for x

The area is 42cm2
- multiply the area by 2 (42 x 2 = 84)
- divide by the base (84  $\div$  12 = 7)

The height of the triangle is 7cm 

Multiple Choice

To find the area of a triangle, simply multiply the base and the height.

• True

• False

Area of a trapezoid

A = $\frac{b_1+b_2}{2}h$  

Trapezoid Example

 $A=\frac{3+8}{2}\ 5$  

 $A=\ \frac{11}{2}\ 5$  

 $A\ =\ 5.5\ x\ 5\ =\ 27.5ft^2$  

Multiple Choice

Find the area of the trapezoid.

• 18 m²

• 165 m²

• 84 m²

• 22.5 m²

Multiple Choice

Find the area.

• 42 yd²

• 84 yd²

• 19 yd²

• 5 yd²

Multiple Choice

What is the area of the trapezoid?

• 24 units²

• 30 units²

• 28 units²

• 20 units2

Multiple Choice

• 41 yds²
• 45 yds²
• 44  yds²
• 43  yds²

Multiple Choice

What does area mean?

• the distance around a shape
• half the distance around a shape
• the amount of space outside a shape
• the amount of space inside a shape

Multiple Choice

Area?

• 108 cm sq
• 60 cm
• 432 cm sq
• 216 cm sq

Multiple Choice

Find the area of a triangle with a height of 4 mm and a base of 6 mm?

• 5 mm squared
• 6 mm squared
• 12 mm squared
• 24 mm squared

Multiple Choice

Area or triangle?

• 20 cm²
• 56 cm²
• 28 cm²
• 27 cm²