How does the dimension of two subspaces relate to their intersection?Possible dimensions of the intersection of two subspacesProve dimension of sum of two subspacesdimension of intersection of subspacesdimension of intersection of a family of subspacesDimension of sum of subspacesIntersection of subspaces and dimensionsCourant–Fischer Theorem Proof [Meyer]. Intersection of two subspaces with same dimension.Dimension of intersection of three subspacesDimension of intersection of 2 distinct subspaces of codimension 1.Intersection of subspaces in $mathbbR^4$

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How does the dimension of two subspaces relate to their intersection?


Possible dimensions of the intersection of two subspacesProve dimension of sum of two subspacesdimension of intersection of subspacesdimension of intersection of a family of subspacesDimension of sum of subspacesIntersection of subspaces and dimensionsCourant–Fischer Theorem Proof [Meyer]. Intersection of two subspaces with same dimension.Dimension of intersection of three subspacesDimension of intersection of 2 distinct subspaces of codimension 1.Intersection of subspaces in $mathbbR^4$













1












$begingroup$



Suppose $U$ and $V$ are subspaces of $mathbb R^8$ such that $dim, U=3$, $dim, V=5$, and $U cup V=mathbb R^8$. Prove that $Uoplus V=mathbb R^8$.




My question is:
How can I, or if I should, use the dimension of $U$ and $V$ to show that their intersection is empty?










share|cite|improve this question











$endgroup$







  • 1




    $begingroup$
    Intersection is not empty. It Just have the zero element.
    $endgroup$
    – dmtri
    Mar 13 at 19:14















1












$begingroup$



Suppose $U$ and $V$ are subspaces of $mathbb R^8$ such that $dim, U=3$, $dim, V=5$, and $U cup V=mathbb R^8$. Prove that $Uoplus V=mathbb R^8$.




My question is:
How can I, or if I should, use the dimension of $U$ and $V$ to show that their intersection is empty?










share|cite|improve this question











$endgroup$







  • 1




    $begingroup$
    Intersection is not empty. It Just have the zero element.
    $endgroup$
    – dmtri
    Mar 13 at 19:14













1












1








1





$begingroup$



Suppose $U$ and $V$ are subspaces of $mathbb R^8$ such that $dim, U=3$, $dim, V=5$, and $U cup V=mathbb R^8$. Prove that $Uoplus V=mathbb R^8$.




My question is:
How can I, or if I should, use the dimension of $U$ and $V$ to show that their intersection is empty?










share|cite|improve this question











$endgroup$





Suppose $U$ and $V$ are subspaces of $mathbb R^8$ such that $dim, U=3$, $dim, V=5$, and $U cup V=mathbb R^8$. Prove that $Uoplus V=mathbb R^8$.




My question is:
How can I, or if I should, use the dimension of $U$ and $V$ to show that their intersection is empty?







linear-algebra vector-spaces






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 13 at 19:18









6005

37k751127




37k751127










asked Mar 13 at 19:11









noobiskonoobisko

715




715







  • 1




    $begingroup$
    Intersection is not empty. It Just have the zero element.
    $endgroup$
    – dmtri
    Mar 13 at 19:14












  • 1




    $begingroup$
    Intersection is not empty. It Just have the zero element.
    $endgroup$
    – dmtri
    Mar 13 at 19:14







1




1




$begingroup$
Intersection is not empty. It Just have the zero element.
$endgroup$
– dmtri
Mar 13 at 19:14




$begingroup$
Intersection is not empty. It Just have the zero element.
$endgroup$
– dmtri
Mar 13 at 19:14










1 Answer
1






active

oldest

votes


















4












$begingroup$

This formula should help:
$$
dim(U + V) = dim(U) + dim(V) - dim(U cap V).
$$

What can you conclude about $dim(U cap V)$? What does that imply about $U oplus V$?






share|cite|improve this answer









$endgroup$








  • 2




    $begingroup$
    P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
    $endgroup$
    – 6005
    Mar 13 at 19:27










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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









4












$begingroup$

This formula should help:
$$
dim(U + V) = dim(U) + dim(V) - dim(U cap V).
$$

What can you conclude about $dim(U cap V)$? What does that imply about $U oplus V$?






share|cite|improve this answer









$endgroup$








  • 2




    $begingroup$
    P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
    $endgroup$
    – 6005
    Mar 13 at 19:27















4












$begingroup$

This formula should help:
$$
dim(U + V) = dim(U) + dim(V) - dim(U cap V).
$$

What can you conclude about $dim(U cap V)$? What does that imply about $U oplus V$?






share|cite|improve this answer









$endgroup$








  • 2




    $begingroup$
    P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
    $endgroup$
    – 6005
    Mar 13 at 19:27













4












4








4





$begingroup$

This formula should help:
$$
dim(U + V) = dim(U) + dim(V) - dim(U cap V).
$$

What can you conclude about $dim(U cap V)$? What does that imply about $U oplus V$?






share|cite|improve this answer









$endgroup$



This formula should help:
$$
dim(U + V) = dim(U) + dim(V) - dim(U cap V).
$$

What can you conclude about $dim(U cap V)$? What does that imply about $U oplus V$?







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Mar 13 at 19:17









60056005

37k751127




37k751127







  • 2




    $begingroup$
    P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
    $endgroup$
    – 6005
    Mar 13 at 19:27












  • 2




    $begingroup$
    P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
    $endgroup$
    – 6005
    Mar 13 at 19:27







2




2




$begingroup$
P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
$endgroup$
– 6005
Mar 13 at 19:27




$begingroup$
P.S. Just a random aside, but the analogous statement for three vector spaces ($dim(U + V + W) = cdots$) is not true; see this famous MathOverflow post.
$endgroup$
– 6005
Mar 13 at 19:27

















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