UNIT 9

: GEOMETR

Y – 6

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: A

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CORNELL NOTES HEADER

Topic: Geometry 6th Grade (Unit 9 pg. 3)

E. Q.: How is the area of a nonrectangular shape calculated?

Name: _____________________________Date: _____________________________Class: _____________________________

Chp. 10 Lesson 2 –Area of a Triangle &Chp. 9 Lesson 2 (my.hrw.com) – Area of a Trapezoid

VOCABULARY

triangle –

A closed plane figure with three straight sides that connect three points.

AREA OF A TRIANGLE

Area of a Triangle: A = ½bh

where b = base (length of any of its sides)

h = height (the perpendicular distance between the side whose length is the base and the vertex opposite that side)

Ex. Find the area of a triangle.

11 ft A = ½bh

= ½(4)(11)

= 22 ft2 4 ft

FINDING AN UNKNOWN DIMENSION

(1) Write the formula for the area of the shape.

(2) Fill in the known values.

(3) Solve for the unknown value.

Ex. The area of a triangle is 36 in2 and the base is 8 in. What is the height of the triangle?

A = 1/2 b h

36 = ½ (8) (h)

36 = 4h

4 4

9 in = h

AREA OF A TRAPEZOID

Formula for the Area of a Trapezoid: A = 1/2h(b1 + b2)

where b1 = base 1 b2 = base 2 h = height

Units are squared.  

6 m

Find the area of the trapezoid.

4.3 m

A = ½h(b1 + b2)

= ½(6)(4.3)(10.5)

= 44.4 m2

10.5 m

GROUP WORK

A builder is adding a patio shaped as shown to the back of a house. What will be the area of the patio?

3 ft. 6 ft.

 

  4 ft.

Area of patio = Area of Triangle + Area of Rectangle

Area of Triangle = ½bh Area of Rectangle = lw

= 1/2(3)(4) = (6)(4)

= 6 ft.2 = 24 ft.2

A = 24 + 6 = 30 ft.2