An acute triangle (or acute-angled triangle) is a triangle with three acute angles (less than 90°). An obtuse triangle (or obtuse-angled triangle) is a triangle with one obtuse angle (greater than 90°) and two acute angles. Since a triangle's angles must sum to 180° in Euclidean geometry, no Euclidean triangle can have more than one obtuse angle.
Acute and obtuse triangles are the two different types of oblique triangles—triangles that are not right triangles because they do not have any right angles (90°).
I would like to know the "why" of trigo of non acute angles in a unit triangle. why is it equals to the reference angle? how did it even come about?
For example, sin 150 degrees. why is it equal to sin 30?
i understand sin 30 because there is a right angle triangle of opposite and hypoteneuse...