significant change of weapon and tactics during hundred years war

During the Hundred years war, military evolution. Weapons, tactics, army structure and the social meaning of war are all rapid changed.
           before hundred years war, heavy armored knight are the main attack power in a war. people belief nothing can penetrate heavy . but after longbow (a powerful bow, it range is twice bigger than normal bow)exist, it can easily Penetrate heavy armor. also heavy armored knight moving speed is very slowly, and they can't do ranger attack, those knight became living target under long range , high penetrate weapon's pressure.
           tactics also rapidly changed during hundred years war, people change their way of fighting from massive, directly attack to small , quickly guerrilla warfare. knight and other noble units has be canceled because they can't afford quickly ,small war,either defend or attack..instead of nobles, mercenary became the main military troops during hundred years war.because training a mercenary only need one month .training a mercenary only need one month meal and 3 gold coin in that time(mercenaries are usually jerk,beggar or young kids)but a knight need ten years and training a knight cost enormous training fee.however, a knight can avenge kill three mercenaries in one fight,but mercenaries is ten times more than those noble, experienced knight.