Which result is used alongside the three trigonometric ratios to solve two-dimensional problems?

1. The three trigonometric ratios are sine, cosine and tangent. 2. Each ratio links one angle to two of the three sides of a right-angled triangle. 3. Sometimes a problem gives two sides and needs the third one before a ratio can be used. 4. The theorem of Pythagoras supplies that missing third side. 5. These three ratios and the theorem of Pythagoras together solve two-dimensional problems. 6. The mid-point theorem belongs to geometry of triangles and says nothing about angles in a right-angled triangle. _Source: Siyavula Mathematics Grade 10 (Everything Maths, CC BY 4.0), Chapter 11: Trigonometry_