1. UNIT 9: GEOMETRY – 6 TH GRADE LESSON 3: AREA OF TRIANGLES & TRAPEZOIDS

2. CORNELL NOTES HEADER Topic: Geometry 6 th 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

3. VOCABULARY triangle – A closed plane figure with three straight sides that connect three points.

4. 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 ft 2 4 ft

5. 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 in 2 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

6. AREA OF A TRAPEZOID Formula for the Area of a Trapezoid: A = 1 / 2 h(b 1 + b 2 ) where b 1 = base 1 b 2 = base 2 h = height Units are squared. 6 m Find the area of the trapezoid. 4.3 m A = ½h(b 1 + b 2 ) = ½(6)(4.3)(10.5) = 44.4 m 2 10.5 m

7. 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