Question

УМОЛЯЮ ЗАВТРА КР xy i yx = (10x•y) + ( 10y+x )

Answer 1

xy=10x+y; yx=10y+x;
1) xy+yx=10x+y+10y+x=11x+11y=11(x+y) – кратне 11;
2) xy–yx=(10x+y)–(10y+x)=10x+y–10y–x=9x–9y=9(x–y) – кратне 9.