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Unit 9: Geometry – 6 th Grade. Lesson 3: Area of Triangles & Trapezoids. Cornell Notes Header. Vocabulary. triangle – A closed plane figure with three straight sides that connect three points. Area of a Triangle. Area of a Triangle: A = ½bh
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Unit 9: Geometry – 6th Grade Lesson 3: Area of Triangles & Trapezoids
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 ftA = ½bh • = ½(4)(11) • = 22 ft2 4 ft
Finding an unknown dimension • Write the formula for the area of the shape. • Fill in the known values. • 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