Areas of Triangles, Parallelograms, & Trapezoids

Rectangle Area = number of square units contained in the figure. Calculated A = lw l w

Rectangle Sometimes referred to as base and height A = bh b h

Parallelogram Especially, when we are looking at a parallelogram A = bh b h

Parallelogram Height is always PERPENDICULAR to the base A = bh b h

Triangles Now let’s consider triangles b h How would we calculate the Area of the triangle?

Triangles A = ½ bh b h

Triangles No matter what the triangle looks like, A = ½ bh. b h h b h b h b

Triangles Folding the corners over shows that the triangle is ½ the rectangle. h b

Trapezoids A = ½ h ( b 1 + b 2 ) h b1b1 b2b2

Sample problems Identify the shape and use the appropriate formula. 8 cm 12 cm

Sample problems A = lw A = 8  12 8 cm 12 cm 96 cm 2

Sample problems Identify the shape and use the appropriate formula. 15’ 9’

Sample problems A = b h A = 15  9 15’ 9’ 135 ft 2

Sample problems Identify the shape and use the appropriate formula. 14”

Sample problems A = s 2 A = in 2 14”

Sample problems Identify the shape and use the appropriate formula. 5cm 24 cm

Sample problems A = ½ b h A = ½ 24  5 5cm 24 cm 60 cm 2

Sample problems Identify the shape and use the appropriate formula. 15 m 12 m 6 m

Sample problems A = ½ h (b 1 + b 2 ) A = ½  6 ( ) 12 m 15 m 6 m 81 m 2

Sample problems Identify the shape and use the appropriate formula. 5 m

Sample problems What is the height? 5 m