Question

cho B= 12 +15 + 18 + 21 + x

tìm x để a] b chia hết cho 3

              b] b ko chia hết cho 3

Answer 1

B = 66 + x 

a) x = 0;3;6;9.

b) x = 10;2;4;5;7;8.

Answer 2

\(B=12+15+18+21+x\)

Ta thấy \(\hept{\begin{cases}12⋮3\\15⋮3\\18⋮3\end{cases}}\)và \(21⋮3\)

a, Để \(B⋮3\Leftrightarrow x⋮3\)

\(\Rightarrow x=\left\{0,3,6,9\right\}\)

b, Để B \(⋮̸\)\(3\)\(\Leftrightarrow x\)\(⋮̸\)\(3\)

\(\Rightarrow x=\left\{1,2,4,5,7,8\right\}\)