Warm Up Problem of the Day Lesson Presentation Lesson Quizzes

Warm Up 1. True or false: If the height of a rectangle equals the base of a parallelogram and the base of the rectangle equals the height of the parallelogram, then the rectangle and the parallelogram have the same area. 2. Find the area of a rectangle with a length of 53 in. and a width of 47 in. True 2,491 in2

Which is a better deal, 3 discs for $5.00 or 4 discs for $7.00? Problem of the Day Which is a better deal, 3 discs for $5.00 or 4 discs for $7.00? 3/$5.00

Learn to find the area of triangles and trapezoids.

You can divide any parallelogram into two congruent triangles You can divide any parallelogram into two congruent triangles. So the area of each triangle is half the area of the parallelogram.

Additional Example 1A: Finding the Area of a Triangle Find the area of the triangle. 1 2 A = bh Write the formula. 1 2 Substitute 20 for b and 12 for h. A = (20 · 12) 1 2 A = (240) Multiply. A = 120 The area is 120 ft2.

Reading Math An altitude of a triangle is a perpendicular segment from one vertex to the line containing the opposite side. The length of the altitude is the height.

Additional Example 1B: Finding the Area of a Triangle Find the area of the triangle. 1 2 A = bh Write the formula. 1 2 Substitute 30 for b and 24 for h. A = (30 · 24) 1 2 A = (720) Multiply. A = 360 The area is 360 in2.

Find the area of the triangle. Check It Out: Example 1A Find the area of the triangle. 1 2 A = bh Write the formula. 1 2 Substitute 5 for b and 8 for h. A = (5 · 8) 8 in. 1 2 5 in. A = (40) Multiply. A = 20 The area is 20 in2.

Find the area of the triangle. Check It Out: Example 1B Find the area of the triangle. 1 2 A = bh Write the formula. A = 1 2 (4 • 24) Substitute 4 for b and 24 for h. 1 2 24 ft 1 2 A = (108) Multiply. 4 ft 1 2 A = 54 The area is 54 in2.

Additional Example 2: Application The diagram shows the section of a forest being studied. What is the area of the section? 1 2 A = bh Write the formula. 1 2 Substitute 43.9 for b. Substitute 16 for h. A = (43.9 • 16) 1 2 A = (702.4) Multiply. A = 351.2 The area is 351.2 km2.

Substitute 48 for b. Substitute 24.5 for h. A = (48 · 24.5) Check It Out: Example 2 The diagram shows the section of a park being studied. What is the area of the section? 24.5 m 48 m 1 2 A = bh Write the formula. 1 2 Substitute 48 for b. Substitute 24.5 for h. A = (48 · 24.5) 1 2 A = (1176) Multiply. A = 588 The area is 588 m2.

Additional Example 3: Finding the Area of a Trapezoid Find the area of the trapezoid. 1 2 A = h(b1 + b2)‏ Use the formula. A = 1 2 · 4(14 + 12 )‏ Substitute 4 for h, 14 for b1, and 12 for b2. 1 2 A = 1 2 · 4(26 )‏ A = 53 Multiply. The area is 53 yd2.

Find the area of the trapezoid. Check It Out: Example 3 12 cm Find the area of the trapezoid. 7 cm 16 cm 1 2 A = h(b1 + b2)‏ Use the formula. 1 2 Substitute 7 for h, 16 for b1, and 12 for b2. A = · 7(16 + 12)‏ 1 2 A = · 7(28)‏ A = 98 Multiply. The area is 98 cm2.

Lesson Quizzes Standard Lesson Quiz Lesson Quiz for Student Response Systems

Lesson Quiz Find the area of each triangle. 1. 3. 2. 39.9 cm2 84 mi2 113 in2 3 4 Find the area of each trapezoid. 4. 22.5 m2

Lesson Quiz for Student Response Systems 1. Find the area of the triangle. A. 48.3 cm2 B. 48.8 cm2 C. 52.3 cm2 D. 58.6 cm2

Lesson Quiz for Student Response Systems 2. Find the area of the triangle. A. 124 m2 B. 134 m2 C. 132 m2 D. 144 m2

Lesson Quiz for Student Response Systems 3. Find the area of the trapezoid. A. 37.2 m2 B. 35.8 m2 C. 33.4 m2 D. 32.6 m2