Prove that T:V->V T^2=T ker(T)+im(T)=V

  • Thread starter specialnlovin
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In summary, we are given a linear map T: V -> V and we want to show that V = ker(T) + im(T). We can break up any element in V that is not in im(T) into a part that is in im(T) and a part that is in ker(T). This can be shown through the equation v = T(v) + (v-T(v)) and the fact that T(v-T(v)) = 0. To prove that the intersection of ker(T) and im(T) is the zero vector, we can use the rank-nullity theorem, but since it may not have been introduced yet, we can show it directly by setting the intersection equal to zero. This then implies that V =
  • #1
specialnlovin
19
0
Let V be a vector space in R and T : V −> V be a linear map such that
T2 = T. Show that V = ker(T)+im(T).
does V = ker(T)  im(T) imply T2 = T? Give a
proof or counter-example.

I really just have no idea how to start this
 
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  • #2
In the first direction, if something in V is not in im(T), can you break it up into a part that is in im(T) and a part that is in ker(T)?
 
  • #3
I think you need to prove that [tex]V=\ker T \oplus I am T [/tex].

This consists out of two parts:

[tex]V=\ker T + I am T [/tex]

I'll give you a hint for this: v=T(v)+(v-T(v))

And you also need to prove

[tex] \ker T \cap I am T = \{0\} [/tex]

This shouldn't prove so hard, I think...
 
  • #4
yes i did mean that, i just have no idea to add the (+) symbol on a computer.
In any case. v=T(v)+(v-T(v))
i know that v-T(v) is in ker(T). is that because v-T(v)=0? But how does this help?
 
  • #5
v-T(v) is in ker T since T(v-T(v))=0.

v=T(v)+(v-T(v)) shows that V=ker T + I am T. Now you only need to show that the intersection in zero.
 
  • #6
show that the intersection is 0 and then use the rank-nullity theorem
 
  • #7
wisvuze said:
show that the intersection is 0 and then use the rank-nullity theorem

Yes, but I don't think he has seen the rank-nullity theorem yet. Since this would make it really trivial...
 
  • #8
wisvuze said:
show that the intersection is 0

How do you do that?
 

1. What does the notation T:V->V mean in this statement?

The notation T:V->V indicates that T is a linear transformation from a vector space V to itself. In other words, T takes in a vector from V and returns another vector in V.

2. How do you prove that T^2 = T?

To prove that T^2 = T, we need to show that T^2(v) = T(v) for all vectors v in V. This can be done by expanding T^2(v) using the definition of a linear transformation and simplifying it to match T(v).

3. What does it mean for ker(T) + im(T) to equal V?

When ker(T) + im(T) = V, it means that every vector in V can be written as a sum of a vector in the kernel of T and a vector in the image of T. In other words, every vector in V can be written as the output of T acting on another vector in V.

4. How can you prove that ker(T) and im(T) are subspaces of V?

To prove that ker(T) and im(T) are subspaces of V, we need to show that they both contain the zero vector, are closed under vector addition, and are closed under scalar multiplication. This can be done using the definitions of a kernel and image of a linear transformation.

5. Can you provide an example of a linear transformation that satisfies T^2 = T and ker(T) + im(T) = V?

Yes, the identity transformation on any vector space V satisfies T^2 = T and ker(T) + im(T) = V. This is because the identity transformation maps every vector to itself, satisfying T^2 = T, and every vector in V can be written as a sum of itself (in im(T)) and the zero vector (in ker(T)), satisfying ker(T) + im(T) = V.

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