What's a proof that the angles of a triangle add up to 180°?
Hmm, in grade school, we took the parallel postulates independently of the sum-of-the-angles-of-a-triangle postulate. How would you prove the parallel postulates from the sum of the angles of a …
Is there a simple method to prove that this triangle is isosceles?
Aug 12, 2025 · Knowing that $\triangle ABC$ is isosceles it's easy to see that AD and AE made the same angle with AF and were then translated and rotated by mirrored amounts, but that's all …
Why sum of interior angles in convex polygon is $ (n-2)\cdot 180$
Feb 26, 2017 · The sum of all the angles in all the triangles equals the sum of the interior angles of the polygon. Notice that the shape has $7$ sides, and we are able to fit $5$ triangles inside it each of …
Calculate height of triangle given angle and base
May 12, 2020 · Calculate height of triangle given angle and base Ask Question Asked 8 years, 4 months ago Modified 5 years, 11 months ago
How do I find the side measures of a triangle, only given the angles ...
Apr 21, 2023 · 2 so you cannot give an exact number as that triangle can be infinitely big or infinitely small and the angles are preserved. Instead you can compare the ratio of the sides by looking at the …
trigonometry - How do I find the angles of a triangle if I only have ...
11 Is it possible to find the angles of a triangle if I only have its sides? If so, how can I achieve this? Regarding my knowledge of triangles: Whilst I was taught trigonometry a few years ago, I cannot for …
geometry - Why is a exterior angle of a triangle equal to the sum of ...
Dec 20, 2018 · In Elements I, 32, Euclid proves the angles of a triangle sum to "two right angles" ($180^o$) by first showing that an exterior angle equals the sum of the two opposite interior angles.
geometry - Can a quadrilateral polygon have 3 obtuse angles ...
Sep 3, 2024 · Here is an example of three obtuse angles which sum to more than 360 degrees and can't form the basis of a quadrilateral - the rays could extend infinitely but will never meet to form a closed …
Langley's Adventitious Angles - Mathematics Stack Exchange
One geometric trick is add a few lines to create an equilateral triangle; then it's a straightforward geometric argument.
Proof of the Exterior Angle Theorem - Mathematics Stack Exchange
Apr 10, 2021 · The exterior angle theorem for triangles states that the sum of “The measure of an exterior angle of a triangle is equal to the sum of the measures of the two interior angles that are not …