Question

Daca x= 3 x a +8 x b + 5 x c si y= 6 x a + b + 4 x c , unde a,b,c ∈ N , aratati ca 9 | ( x+y+z ) si (x+y+z) ≡ (a+b+c)

Answer 1

x+y=3a+8b+5c+6a+b+4c=9a+9b+9c
x+y=9(a+b+c)=>9|(x+y) si(x+y) $\vdots$(a+b+c)