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Example Questions
Example Question #501 : Operations And Properties
There is a relationship between the dimension of the domain and the dimension of the null space and the rank of a function. The relationship is
where is the dimension of the domain,
is the dimension of the null space,
and is the rank.
Let be linear map such that and the rank is 3. What is the dimension of the null space of ?
6
3
0
2
8
2
The answer is .
The dimension of the domain is .
The rank of f is .
Plug these into the equation given above to get
Therefore, the dimension of the null space is .
Example Question #502 : Operations And Properties
There is a relationship between the dimension of the domain and the dimension of the null space and the rank of a function. This question is on that.
Let be linear map with a rank of 6 and a null space with dimension . What is the dimension of the domain of ?
Use the formula
where is the dimension of the domain,
is the dimension of the null space,
and is the rank.
From the problem statement, we know and . Therefore
Example Question #503 : Operations And Properties
Let be a linear mapping such that . What is the largest possible rank of ?
The answer is . The largest possible rank of a linear map is always the dimension of the domain. Let's see why that is.
Use the formula
where is the dimension of the domain,
is the dimension of the null space,
and is the rank.
From the problem statement, we know and is largest when . Hence
Example Question #21 : Linear Mapping
Let be a function such that . Is it possible for to have a rank of and a null space with dimension ?
not enough information
no
yes
no
The rank and the dimension of the null space must add up to the dimension of the domain from the formula
where is the dimension of the domain,
is the dimension of the null space,
and is the rank.
For this problem the dimension of the domain () is . So
From the problem statement, we want to consider and But if we plug this into the formula we get
Hence the equation for dimension doesn't hold.
Example Question #21 : Linear Mapping
A mapping is said to be onto (sometimes called surjective) if it's image is the entire codomain.
Is the linear map such that onto?
Yes
Not enough information
No
Yes
Yes, is onto because any vector in the codomain, , is the image of a vector from the domain.
Example Question #22 : Linear Mapping
A mapping is said to be onto (sometimes called surjective) if it's image is the entire codomain.
Is the linear map such that onto?
(This map is sometimes called a projection, specifically a projection onto the xy plane.)
No
Not enough information
Yes
Yes
This mapping is onto. For any given vector in the codomain, , there is a corresponding vector in the domain, .
Example Question #23 : Linear Mapping
Is the linear map such that onto?
(Note this is sometimes called the identity map because it maps every vector to itself)
Not enough information
No
Yes
Yes
The answer is yes, the mapping is onto. The image of is which is the codomain.
Example Question #504 : Operations And Properties
A mapping is said to be onto (sometimes called surjective) if it's image is the entire codomain.
Is the linear map such that onto?
Not enough information
No
Yes
No
First we need to find the image of Any vector in the image of has the form .
Treat and like arbitrary constants. Then the image of is the subspace spanned by the set of vectors This subspace has a basis of 2 vectors. Therefore it has dimension of .
The image of does not span the whole codomain, , because the image does not have the same dimension as the codomain, .
Another way to do this problem is recognize that the domain,, has dimension . Therefore, the linear map can have an image of with dimension of at most 2. But the codomain has dimension . Since , can't be onto.
Example Question #24 : Linear Mapping
A mapping is said to be onto (sometimes called surjective) if it's image is the entire codomain.
Is the linear map such that onto?
(Note this is called the zero mapping)
Not enough information
Yes
No
No
No, is not onto. This is because the image of is only the zero vector, not all of
Example Question #25 : Linear Mapping
A mapping is said to 1-to-1 (sometimes called injective) if no two vectors in the domain go to the same vector in the image of the mapping.
Is the linear map such that 1-to1?
Not enough information
No
Yes
Yes
The linear map, , is 1-to-1 because no vector in the codomain is the output of two different vectors in the domain.
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