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Linear Algebra, Theory And Applications, 2012a

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220 VECTOR SPACES AND FIELDS<br />

7. Let M = { u =(u 1 ,u 2 ,u 3 ,u 4 ) ∈ R 4 : |u 1 |≤4 } . Is M a subspace? Explain.<br />

8. Let M = { u =(u 1 ,u 2 ,u 3 ,u 4 ) ∈ R 4 :sin(u 1 )=1 } . Is M a subspace? Explain.<br />

9. Suppose {x 1 , ··· , x k } is a set of vectors from F n . Show that 0 is in span (x 1 , ··· , x k ) .<br />

10. Consider the vectors of the form<br />

⎧⎛<br />

⎨<br />

⎝<br />

⎩<br />

2t +3s<br />

s − t<br />

t + s<br />

⎞ ⎫<br />

⎬<br />

⎠ : s, t ∈ R<br />

⎭ .<br />

Is this set of vectors a subspace of R 3 ? If so, explain why, give a basis for the subspace<br />

and find its dimension.<br />

11. Consider the vectors of the form<br />

⎧⎛<br />

⎞<br />

2t +3s + u<br />

⎪⎨<br />

⎫⎪ ⎜ s − t<br />

⎬<br />

⎟<br />

⎝ t + s ⎠<br />

⎪⎩<br />

: s, t, u ∈ R .<br />

⎪ ⎭<br />

u<br />

Is this set of vectors a subspace of R 4 ? If so, explain why, give a basis for the subspace<br />

and find its dimension.<br />

12. Consider the vectors of the form<br />

⎧⎛<br />

⎞<br />

2t + u +1<br />

⎪⎨<br />

⎫⎪ ⎜ t +3u<br />

⎬<br />

⎟<br />

⎝ t + s + v ⎠<br />

⎪⎩<br />

: s, t, u, v ∈ R .<br />

⎪ ⎭<br />

u<br />

Is this set of vectors a subspace of R 4 ? If so, explain why, give a basis for the subspace<br />

and find its dimension.<br />

13. Let V denote the set of functions defined on [0, 1]. Vector addition is defined as<br />

(f + g)(x) ≡ f (x)+g (x) and scalar multiplication is defined as (αf)(x) ≡ α (f (x)).<br />

Verify V is a vector space. What is its dimension, finite or infinite? Justify your<br />

answer.<br />

14. Let V denote the set of polynomial functions defined on [0, 1]. Vector addition is<br />

defined as (f + g)(x) ≡ f (x)+g (x) and scalar multiplication is defined as (αf)(x) ≡<br />

α (f (x)). Verify V is a vector space. What is its dimension, finite or infinite? Justify<br />

your answer.<br />

15. Let V be the set of polynomials defined on R having degree no more than 4. Give a<br />

basis for this vector space.<br />

16. Let the vectors be of the form a + b √ 2wherea, b are rational numbers and let the<br />

field of scalars be F = Q, the rational numbers. Show directly this is a vector space.<br />

What is its dimension? What is a basis for this vector space?<br />

17. Let V be a vector space with field of scalars F and suppose {v 1 , ··· , v n } is a basis for<br />

V .NowletW also be a vector space with field of scalars F. LetL : {v 1 , ··· , v n }→<br />

W be a function such that Lv j = w j . Explain how L can be extended to a linear<br />

transformation mapping V to W in a unique way.

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