Answer :
[tex]\mathbf{Au}=\mathbf0[/tex]
[tex]\mathbf{Av}=\mathbf0[/tex]
[tex]\implies\mathbf{Au}+\mathbf{Av}=\mathbf0[/tex]
[tex]\implies\mathbf A(\mathbf u+\mathbf v)=\mathbf0[/tex]
Multiplying by scalars [tex]c,d[/tex] won't change this fact.
[tex]\mathbf{Av}=\mathbf0[/tex]
[tex]\implies\mathbf{Au}+\mathbf{Av}=\mathbf0[/tex]
[tex]\implies\mathbf A(\mathbf u+\mathbf v)=\mathbf0[/tex]
Multiplying by scalars [tex]c,d[/tex] won't change this fact.