Time for More Triangles

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SWBAT apply theorems about interior and exterior of triangles to rigorous problems.

Big Idea

Students will use detective skills and their knowledge of triangles to hunt down missing angle measurements.

Do Now

10 minutes

For the do now, students will review key concepts relating to angles and triangles like complements and finding a third angle in a triangle.  Question #3 also reviews factoring, an algebraic concept which will be required to solve questions in the notes and homework.

We also will use corollaries in this lesson, and teachers may want to review this key word with students prior to the pair-share activity. 

Pair-Share and Exploration focus on Mathematical Practices

25 minutes


15 minutes

These five practice questions can be done in a scaffolded manner - example one could be lead by the teacher and then example two can be done by a student at the board (MP3).  Example 3 is the trickiest concept because it requires students to factor first then solve.  The other remaining examples are a review of prior knowledge about angles and triangles. 

Pre-Proof Practice

5 minutes

If you have time left in class, the Regent's Prep website reviews a host of geometric concepts that have been covered so far in the course (right angles, bisectors, perpendicular lines).  The website allows teachers to show a photo of a geometric situation with a given statement.  Then, students can write down what the "statement" and "reason" are for each - and check with the website's drop-down menu. Since we will re-introduce formal and flow proofs next lesson, this is a great review and prep for students (MP8).



10 minutes

If you have time in class, students can work on the activity or can work on this assignment for homework (MP #8).  The questions are taken from regentsprep.org/geometry, which is also a great resource for absent students.

Exit Ticket

10 minutes

Students can complete this exit ticket to measure their knowledge of applying exterior angle theorem.  This exit ticket also requires students to use their algebra skills!