Algebra: Chapter 10 TEST!
Math-8, Chapter 11-4, p 568
Triangles
Triangles can be classified by their angles or their sides or both. Every angle has 2 acute angles and the 3rd angle can be used to classify the triangle. Triangles always have 180°!
- Acute: has 3 acute angles
- Right: has 1 right angle
- Obtuse: has one obtuse angle
- Equilateral: has 3 congruent sides
- Isosceles: has at least 2 congruent sides
- Scalene: has no congruent sides
If you know 2 of the 3 angles in a triangle, you can always find the other one by subtracting the sum of the 2 from 180°. For example:
If `∠a = 36°` and `∠b = 32°`, then `∠c = 180° − 36° − 32°` or `∠c = 112°`
If `∠a = x°` and `∠b = 80°`, and `∠c = (x + 10)°`, then `180° = x + x + 80 + 10` or `180 = 2x + 90` or `180 − 90 = 2x` or `90 = 2x` and finally `x=45`. The angles are then 45°, 55° and 80°!