Definition/Procedure Example 4.3 Triangles Perimeter and Area of a Triangle A triangle is a closed fi gure with exactly three sides. The perimeter of a triangle is the distance around the triangle. The area, A, of a triangle is 1) Area 1 2 base height or 2) A 1 2 bh where b the length of the base and h the height. (p. 308) Find a) the perimeter and b) the area of this triangle. 4 in. 5 in. 10 in. 8 in. a) To fi nd the perimeter, add the lengths of the sides of the triangle. P 8 in. 5 in. 10 in. 23 in. b) To fi nd the area, we will use A 1 2 bh. A 1 2 (10 in.)(4 in.) Substitute the values. A 20 in2 Multiply. The Sum of the Angle Measures in a Triangle The measures of the angles in a triangle add up to 180. (p. 312) B A C mA mB mC 180 Classifying Triangles An acute triangle is one in which all three angles are acute. A right triangle contains one right, or 90, angle. An obtuse triangle contains one obtuse angle. An equilateral triangle has three sides of equal length. An isosceles triangle has two sides of equal length. A scalene triangle has no sides of equal length. (p. 313) Acute triangle: Right triangle: Obtuse triangle: Obtuse angle Equilateral triangle: 5 cm 5 cm 5 cm Isosceles triangle: Scalene triangle: 346 CHAPTER 4 Basic Geometry Concepts and Algebra www.mhhe.com/messersmith
messersmith_power_prealgebra_1e_ch4_7_10
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