Seeing Right Triangles

Sometimes you are given a triangle that does not have a \(90^\circ\) angle; therefore, you cannot use the primary trigonometric ratios directly to solve the problem. These non-right angle triangles are called oblique triangles. Oblique triangles can be acute or obtuse. An obtuse oblique triangle contains one obtuse angle.

To work around this, you can turn the one oblique triangle into two right triangles by inserting an altitude, which extends from a vertex of the triangle to meet the opposite side at a right angle. In the diagrams shown, the red lines are altitudes.