2 times 2 equals 4
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Matrix A =
(a b)
(c d)
Matrix B =
(w x)
(y z)
Then AB =
(aw+by ax+bz)
(bw+dy bx+dz)
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I assume since you're asking if 2x2 invertible matrices are a "subspace" that you are considering the set of all 2x2 matrices as a vector space (which it certainly is). In order for the set of 2x2 invertible matrices to be a subspace of the set of all 2x2 matrices, it must be closed under addition and scalar multiplication. A 2x2 matrix is invertible if and only if its determinant is nonzero. When multiplied by a scalar (let's call it c), the determinant of a 2x2 matrix will be multiplied by c^2 since the determinant is linear in each row (two rows -> two factors of c). If the determinant was nonzero to begin with c^2 times the determinant will be nonzero, so an invertible matrix multiplied by a scalar will remain invertible. Therefore the set of all 2x2 invertible matrices is closed under scalar multiplication. However, this set is not closed under addition. Consider the matrices {[1 0], [0 1]} and {[-1 0], [0 -1]}. Both are invertible (in this case, they are both their own inverses). However, their sum is {[0 0], [0 0]}, which is not invertible because its determinant is 0. In conclusion, the set of invertible 2x2 matrices is not a subspace of the set of all 2x2 matrices because it is not closed under addition.
how to multiply two sparse matrices
Closed . . . .A+
The matrix multiplication in c language : c program is used to multiply matrices with two dimensional array. This program multiplies two matrices which will be entered by the user.
Order of operations--Parenthesis, Exponents, Multiplication, Division, Addition, Subtraction. 15-2x2 (fifteen minus two times two) 15-4 11