A lesson for finding missing angles in a right triangle.

Subjects:

Mathematics > General

Mathematics > Geometry

Mathematics > Trigonometry

Education Levels:

Grade 9

Grade 10

Grade 11

Grade 12

Keywords:

geometry curriculum curricula right triangles inverse trigonometric functions function triangle

Language:

English

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License Deed:

Creative Commons Attribution 3.0

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Aim: How do we find missing angle measures given two side lengths in a right triangle?

Learning objectives: Students will be able to solve a right triangle (find all missing angles and side lengths) given either two side lengths of the right triangle or one side length and one acute angle.

Prerequisite knowledge: Students should be familiar with the sine, cosine, and tangent ratios. Students should know the Pythagorean Theorem. Students should know that the sum of the angles in a triangle is 180°.

Motivational problem: 1. If C = 90°, c = 25, and b = 20, what is a? 2. If A = 30° and C = 90°, what is B?

Key ideas: If sinx = a/b then x = sin¯¹(a/b). An inverse function "undoes" the trigonometric function just as addition "undoes" subtraction and multiplication "undoes" division.

Important questions: What information is need to solve a triangle? What is an inverse function?