Mathematics for Applied Sciences (Osnabrück 2011-2012)/Part I/Exercise sheet 6
- Warm-up-exercises
Compute the following product of matrices
Compute, over the complex numbers, the following product of matrices
Determine the product of matrices
where the -th standard vector (of length ) is considered as a row vector, and the -th standard vector (also of length ) is considered as a column vector.
Let be an - matrix. Show that the matrix product of with the -th standard vector (regarded as a column vector) is the -th column of . What is , where is the -th standard vector (regarded as a row vector)?
Compute the product of matrices
according to the two possible parentheses.
For the following statements we will soon give a simple proof using the relationship between matrices and linear maps.
Show that the multiplication of matrices is associative. More precisely: Let be a field, and let be an -matrix, an -matrix, and a -matrix over . Show that .
For a matrix we denote by the -th product of with itself. This is also called the -th power of the matrix.
Compute, for the matrix
the powers
Let be a field, and let and be vector spaces over . Show that the product set
is also a -vector space.
Let be a field, and an index set. Show that
with pointwise addition and scalar multiplication, is a -vector space.
Let be a field, and let
be a system of linear equations over . Show that the set of all solutions of this system is a linear subspace of . How is this solution space related to the solution spaces of the individual equations?
Show that the addition and the scalar multiplication of a vector space can be restricted to a linear subspace, and that this subspace with the inherited structures of is a vector space itself.
Let be a field, and let be a -vector space. Let be linear subspaces of . Prove that the union is a linear subspace of if and only if or .
- Hand-in-exercises
Exercise (3 marks)
Compute, over the complex numbers, the following product of matrices
Exercise (3 marks)
We consider the matrix
over a field . Show that the fourth power of is , that is,
Exercise (3 marks)
Let be a field, and let be a -vector space. Show that the following properties hold (for and ).
- We have .
- We have .
- We have .
- If and , then .
Exercise (3 marks)
Give an example of a vector space and of three subsets of that satisfy two of the subspace axioms, but not the third.