Разложи на множители (u+20v)^2−(20u+v)^2
(u+20v -(20u+v))(u+20v+ 20u+v)= (u+20v-20u-v)(21u +21v)=(19v-19u)(21u+21v)= 19*21(v-u)(v+u)= =399(v-u)(v+u)