#1. Let ? be the set of all diagonal matrices in ?22. Is ? a subspace of ?22? Justify your conclusion (write a proof).
1. Let A =
a |
0 |
0 |
b |
and B =
c |
0 |
0 |
d |
where a,b,c,d are arbitrary real numbers ,be 2 arbitrary diagonal matrices inW, and let k be an an arbitrary real scalar.
Then A+B =
a+c |
0 |
0 |
b+d |
Now, A+B being a 2x2 diagonal matrix, belongs to W . Hence, W is closed under vector addition.
Also, kA =
ka |
0 |
0 |
kb |
Now, kA being a 2x2 diagonal matrix, belongs to W . Hence, W is closed under scalar multiplication.
Further, the 2x2 zero matrix, being a diagonal matrix, belongs to W .
Hence W is a vector space, and, therefore, a subspace of M22.
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