Question 12***+Adding a vector already in a span does not change the span. Illustrate using \((1,0),(0,1),(1,1)\).
Question 18*****A student says two vectors in \(\mathbb R^3\) can span all of \(\mathbb R^3\) if they are long enough. Explain the error.
Question 20*****Prove that if \(T\subseteq S\), then \(\operatorname{span}(T)\subseteq\operatorname{span}(S)\).