1) The document demonstrates how to prove trigonometric identities using sum and difference formulas by relating trigonometric functions of two angles (A and B) to the functions of their sum or difference. 2) It derives the identities cos(A+B)=cosAcosB - sinAsinB and sin(A+B)=sinAcosB + cosAsinB through using distance and angle formulas in a triangle. 3) Further identities like tan(A+B), tan(A-B) are derived by substituting the expressions for sin(A+B) and cos(A+B) in the definition of tangent.