6.7 Areas of Triangles and Quadrilaterals. Geometry Mrs. Spitz Spring 2005. Objectives:. Find the areas of squares, rectangles, parallelograms and triangles. Find the areas of trapezoids, kites and rhombuses. Assignment. pp. 376-378 #3-43. Skip 39 and 40. Using Area Formulas.
pp. 376-378 #3-43. Skip 39 and 40.
You know this one and you have since kindergarten. Since you do the others should be a breeze.Area Theorems
A = bh
A = bh
A = ½ bh
The area of a parallelogram is the area of a rectangle with the same base and height.Justification
The area of a triangle is half the area of a parallelogram with the same base and height.Justification
A= ½ bh Formula for the area of a triangle
2A=bh Multiply both sides by 2.
2A=h Divide both sides by b.
h=2A = 2(12) = 24 = 4
b 6 6
The height of the triangle is 4.
Solution: Using the formula from Ex. 2, the height is
h = 2(52) = 104 =8
Here are a few triangles with these dimensions:Ex. 3: Finding the Height of a Triangle
A = ½ h(b1 + b2)Areas of Trapezoids
A = ½ d1d2Areas of Kites
A = ½ d1 d2Areas of Rhombuses
Substitute 4 for h, 3 for b1, and 7 for b2 to find the area of the trapezoid.
A = ½ h(b1 + b2) Formula for area of a trapezoid.
A = ½ (4)(3 + 7 ) Substitute
A = ½ (40) Simplify
A = 20 Simplify
The area of trapezoid WXYZ is 20 square units
Method 1: Use the formula for the area of a rhombus d1 = BD = 30 and d2 = AC =40Ex. 5 Finding the area of a rhombus