In: Advanced Math
a. Prove that y=sin(x) is a subspace of R^2
b. Prove that a set of 2x2 non invertible matrices a subspace of all 2x2 matrices
b. A 2 2 is said to be non invertible if and only if determinant is zero .
Let S = set of all 2 2 non - invertible matrix .
Suppose A ,B S
det (A) = 0 and Det (B) = 0
Now det(AB) = det(A) . det(B) =0 .0 =0
AB S
Also det (cA) = c2 det (A) = c2 . 0 = 0
cA S
So A , B S then AB S and cA S
Hence S i.e., set of all 2 2 non invertible matrix forms a subspace set of all 2 2 matrices .
a. y = sin (x) is not forms a subspace of .
Because every proper suspace of is a straight line through origin but sin(x) is not .
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If you have any doubt or need more clariication at any step please comment .