Mr. Ohashi's Math 8 Website

Eighth Grade Math at Eckstein Middle School

Tag Archives: interior angle sums

Tuesday, 6/13: Equal Angles (Day 11 of 14)

Learning Target: Use angle relationships to determine unknown angle measures.
Handouts: Equal Angles (Turn in: Wed, 6/14)

Today we learned a few new symbols. The symbols drawn on the angles below show that the angles are equal in measure. Notice that in the parallelogram, one pair of angles is equal, but not equal to the other pair of angles.

If you have a regular polygon, all side lengths are equal and all angles are equal (like the pentagon below). We can actually find the measure of each of the interior angles using the interior angle sum formula. Since all of the angles are equal, divide the interior angle sum by the number of angles!

Third period should finish #1-8. Fourth & fifth period should finish #1-6. Don’t forget that we have a quiz on Friday!

Monday, 6/12: Using Interior Angle Sums (Day 10 of 14)

Learning Target: Use the interior angle sum formula to find unknown angle measures.
Handouts: Using Interior Angle Sums (Turn in: Tues, 6/13)

Today we used the interior angle sum formula that we came up with last week. For example, if we know how many sides a polygon has, we can determine the interior angle sum (see the first example below). But today we also had to apply the formula to solve problems. In the second example below, we know the interior angle sum of a polygon, but we want to know how many sides it must have. We can set up and solve an algebra equation using the formula.

Almost every single problem on today’s assignment needed the interior angle sum formula in some way! Your homework is to finish #1-13. Also, we have a quiz on Friday!

Friday, 6/9: Class Expectations Posters

Learning Target: Make posters to review the class expectations.
Handouts: None

All year, you have been seeing the class expectations posters that last year’s students made. Today, you got a chance to make one with your table group. Remember, the best of the best will be put up on the wall for next year’s students to look at every day!

There is no homework. Have a great weekend!

Thursday, 6/8: Interior Angle Sums (Day 9 of 14)

Learning Target: Explore polygons to find a formula for the interior angle sum of any polygon.
Handouts: Interior Angle Sums (Turn in: Fri, 6/9)

Today we explored the interior angles of polygons. We know that the interior angles of any triangle always add up to 180 degrees. This is called an interior angle sum… because it is all of the interior angles added together (the sum!). Using our knowledge of triangles, we can then find the interior angle sum of any polygon by cutting the polygon up into triangles! To find the interior angle sums, pick a vertex (corner) and draw lines to other corners to form triangles. Since each triangle has 180 degrees in it, the interior angle sum of the polygon will be the number of triangles times 180 degrees.

We did the first part of the assignment together and found that there is a formula for finding this information without cutting up the shapes! If we take the number of sides of subtract 2, we know how many triangles are in the polygon. Then we can multiply that number of 180 to find the interior angle sum! We wrote that formula in our notes:

Your homework is to finish #1-5.