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Unit 1, Lesson 2, Investigation 2: The Law of Sines

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Ithaca High School Lesson Plans

Content Standards and Benchmarks:

II,3,1: Select and use appropriate tools; make accurate measurements using both metric and common units, and measure angles in degrees and radians.

          II,3,5: Use proportional reasoning and indirect measurements including applications of trigonometric ratios, to measure inaccessible distances and to determine derived measures such as density.



After a class discussion regarding the properties of triangles and working through a trigonometric (trig) proof, students will be able to justify their algebraic steps for solving for trig values with definitions, theorems, and properties. 

After showing students that using the Law of Sines is more efficient that doing a proof for each trig problem, student will be able to apply the Law of Sines to solve trig problems.


Anticipatory Set:

          Warm-up: “When do we use the Pythagorean Theorem?”

              Given 2 sides find the 3rd

              Gives a length

              No angles involved

Class Discussion: I have a secret and a trick for your but we have

                 to work through some SCARY stuff first. We need to do a

                 proof!  Proofs are scary because:

              No set process

              Higher order thinking

              Can’t check work

              Smart people do it

v             They really aren’t all that bad!

v             Let’s do one!



     How to do proofs: Justify your algebra with properties,

definitions, theorems, and Laws.

     How to apply the Law of Sines

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