Consider triangles AOD and BCO formed by intersecting diagonals and trapezoid bases.
Because each side of a triangle is less than the sum of the other two sides, then:
AD <AO + OD (for triangle AOD) and BC <BO + OC (for triangle BCO).
Let us add up the inequalities.
AD + BC <AO + OD + BO + OC;
AD + BC <(AO + OC) + (OD + BO);
AD + BC <AC + BD.
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.