- #1
danago
Gold Member
- 1,123
- 4
Let [tex]\vec{u},\vec{v},\vec{w}[/tex] be fixed vectors in Rn. Define S to be the set of all vectors in Rn which are linear combinations of the form [tex]k_1 \vec{u}+k_2 \vec{v}+3 \vec{w}[/tex], where [tex]k_1,k_2 \in R[/tex]. Is S a subspace of Rn?
Im a little stuck with this one. I've tried defining two vectors, [tex]\vec{x},\vec{y} \in S[/tex] and then forming a linear combination of the two, to get:
[tex]
a\overrightarrow x + b\overrightarrow y = (ak_1 + bc_1 )\overrightarrow u + (ak_2 + bc_2 )\overrightarrow v + (3a + 3b)\overrightarrow w
[/tex]
Where:
[tex]
\begin{array}{l}
\overrightarrow x = k_1 \overrightarrow u + k_2 \overrightarrow v + 3\overrightarrow w \\
\overrightarrow y = c_1 \overrightarrow u + c_2 \overrightarrow v + 3\overrightarrow w \\
\end{array}
[/tex]
Thats where I am lost; I am not even sure if I've taken the right approach. From this i can see that the linear combination of vectors x and y results in an expression containing linear combinations of vectors u and v, but its the w vector that's causing me problems.
Any hints are greatly appreciated
Thanks,
Dan.
Im a little stuck with this one. I've tried defining two vectors, [tex]\vec{x},\vec{y} \in S[/tex] and then forming a linear combination of the two, to get:
[tex]
a\overrightarrow x + b\overrightarrow y = (ak_1 + bc_1 )\overrightarrow u + (ak_2 + bc_2 )\overrightarrow v + (3a + 3b)\overrightarrow w
[/tex]
Where:
[tex]
\begin{array}{l}
\overrightarrow x = k_1 \overrightarrow u + k_2 \overrightarrow v + 3\overrightarrow w \\
\overrightarrow y = c_1 \overrightarrow u + c_2 \overrightarrow v + 3\overrightarrow w \\
\end{array}
[/tex]
Thats where I am lost; I am not even sure if I've taken the right approach. From this i can see that the linear combination of vectors x and y results in an expression containing linear combinations of vectors u and v, but its the w vector that's causing me problems.
Any hints are greatly appreciated
Thanks,
Dan.