Răspuns :
xy * a+ yx* b=ab *x+ba * y
(10x+y) *a+(10y+x)*b=(10a+b) * x+ (10 b+ a) * y
(11x+11y) *a*b=(11a+11b) * x *y
10x+10y=10a+10b
10(x+y)=10(a+b)
(10x+y) *a+(10y+x)*b=(10a+b) * x+ (10 b+ a) * y
(11x+11y) *a*b=(11a+11b) * x *y
10x+10y=10a+10b
10(x+y)=10(a+b)