a: =>n+3+12 chia hết cho n+3
=>\(n+3\in\left\{1;-1;2;-2;3;-3;4;-4;6;-6;12;-12\right\}\)
hay \(n\in\left\{-1;-4;-1;-5;0;-6;1;-7;3;-9;9;-15\right\}\)
b: =>n-2-7 chia hết cho n-2
=>\(n-2\in\left\{1;-1;7;-7\right\}\)
hay \(n\in\left\{1;3;9;-5\right\}\)
c: =>5n+15+13 chia hết cho n+3
=>\(n+3\in\left\{1;-1;13;-13\right\}\)
hay \(n\in\left\{-2;-4;10;-16\right\}\)
d: =>n^3+3n^2-n^2+9 chia hết cho n+3
=>(n+3)(n^2-n+3) chia hết cho n+3(luôn đúng)
e: =>6n+3+12 chia hết cho 2n+1
=>\(2n+1\in\left\{1;-1;2;-2;3;-3;4;-4;6;-6;12;-12\right\}\)
hay \(n\in\left\{0;-1;\dfrac{1}{2};-\dfrac{3}{2};1;-2;\dfrac{3}{2};-\dfrac{5}{2};\dfrac{5}{2};-\dfrac{7}{2};\dfrac{11}{2};-\dfrac{13}{2}\right\}\)
