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Geometry

Welcome to the guide types of angles and triangles

This is an introductory lesson on Triangles. If you feel that you have a good understanding of triangles, test your knowledge to confirm you know 100% of the material. If not, do not worry and follow the lesson closely!

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Background Concepts:

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https://www.youtube.com/watch?v=BTnAlNSgNsY (Supplementary and Complementary Angles)

Types Of Angles:

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https://www.khanacademy.org/math/basic-geo/basic-geo-angle/basic-geo-angle-types/v/acute-right-and-obtuse-angles (Video for visual learners)

https://www.mathsisfun.com/angles.html (This is helpful because you can play around with the angles)

Triangles:

https://www.youtube.com/watch?v=1k0G-Y41jRA

https://www.mathsisfun.com/triangle.html (Notice what happens to the other two angles when you change one angle of the triangle)

https://www.khanacademy.org/math/geometry/hs-geo-trig/hs-geo-special-right-triangles/v/45-45-90-triangles (Special right triangles PART 1)

https://www.khanacademy.org/math/geometry/hs-geo-trig/hs-geo-special-right-triangles/v/intro-to-30-60-90-triangles (Special right triangles PART 2)

WAIT: Can there be more than one obtuse angle in a triangle? What about right angles? Acute angles?

The angles of a triangle add up to 180 degrees (remember the formula 180 * (n-2)).

Since obtuse angles are greater than 90 degrees, two of these angles would add up to be greater than 180. Since 2 right angles add up to 180 degrees, it doesn’t leave room for a third angle. Therefore, you cannot have two obtuse or two right angles in a triangle. However, you can have two acute angles because they add up to less than 180 degrees.

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Practice:

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https://www.khanacademy.org/math/basic-geo/basic-geo-angle/vert-comp-supp-angles/e/complementary_and_supplementary_angles (Supplementary and complementary angles)

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https://www.khanacademy.org/math/basic-geo/basic-geometry-shapes/basic-geo-classifying-triangles/e/identifying-triangles-by-angles (Classifying triangles)

https://www.khanacademy.org/math/basic-geo/basic-geometry-shapes/triangle-angles/e/triangle_angles_1 (Find the missing angle)

https://www.khanacademy.org/math/geometry/hs-geo-trig/hs-geo-special-right-triangles/e/pythagorean_theorem_2 (Special right triangles)

https://www.ixl.com/math/geometry/special-right-triangles (Slightly more challenging, you can stop if you get to a problem that requires trigonometry (which would be giving you three angles but no side lengths)

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Check for Understanding (final review):

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*To look at the answers, click here*

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Congrats on reaching the end of this lesson. If you did not understand any concept be sure to go back through and review, so that you can be fully prepared. We learn the most from our mistakes so don’t be disheartened by them. When you feel that you are ready, go ahead and take a little break. Then come back and move onto another section!