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UNIT 9
: GEOMETR
Y – 6
TH
GRADE
L ES
SO
N 3
: A
RE
A O
F TR
I AN
GL E
S &
TR
AP
EZ
OI D
S
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