th grade math Area of Triangles

Objective To find the area of triangles Why? To know how to use formulas and evaluate variable expressions using the order of operations. To further your knowledge of geometry and measurement.

California State Standards AF 3.1: Use variables in expressions describing geometric quantities … (e.g., A = ½ bh, …- the formula for … the area of triangles …) AF 3.2: Express in symbolic form simple relationships arising from geometry. MR 1.1: Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, … and observing patterns. MR 1.3: Determine when and how to break a problem into simpler parts. MR 2.5: Express the solution clearly and logically by using the appropriate mathematical notation and terms and clear language; support solutions with evidence in both verbal and symbolic work MR 3.2: Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving similar problems.

Vocabulary Triangles – ½ of a quadrilateral Parallelogram = b x h Triangle = ½ b x h

How to Solve Area of Triangles 1)Observe or draw the triangle figure. Be sure all measurements are in equal labels. 2) Write out the formula: ½ x (l x w) or ½ (b x h) 3) ½ either the l or the w. Or multiply l and w and then ½. 4) Check work and add label ² to answer. Find the area of the parallelogram. Base = 30 yd, Height = 20 yd A = 30 x 20 A = 600 yd ² Find the area of the triangle. You can split the parallelogram into 2 triangles. A = ½ (30 x 20) or 30 x (1/2 x 20) = ½ x 600 = 30 x 10 = 300 yd ²

Try It! 1)Triangle: 9 m, 18 m 2)Triangle: 9 ft, 18 ft 3)Triangle: 24 in, 6 in 4)Triangle: 10 cm, 20 cm 5) Triangle: base = 1.5 m, height 850 cm 1)Triangle: 9 m, 18 m = 9 x 9 = 81 m ² 2) Triangle: 9 ft, 18 ft = 9 x 9 ft ² = 81 m ² 3) Triangle: 24 in, 6 in = 12 x 6 = 72 in ² 4) Triangle: 10 cm, 20 cm = 10 x 10 = 100 cm ² 5)Triangle: base = 1.5 m, height 850 cm = 1.5 m x 4.25 m = m ²

Objective Review To find the area of triangles Why? You now know how to use formulas and evaluate variable expressions using the order of operations. You have furthered your knowledge of geometry and measurement. The area of a triangle is ½ times the base times the height (or ½ times the height times the base)

Independent Practice Complete problems Copy original problem first. Show all work! If time, complete Mixed Review: If still more time, work on Accelerated Math.