3. Let n = 4 (we choose 4 for calculation simplicity, but the following are true for arbitrary n). Let S: R →R be a linear transformation such that S(In) = n, and S(AB) = S(BA) for all n x n matrices A, B. In this problem, we will show that S and tr (defined in problem 2) are the same linear transformation. %3D (A) Let i e {1, 2, .. ,n}. Let eii € Rn² be the matrix with 1 on the (i, i)-entry, and 0 everywhere else. Calculate that S(eu) = 1. Hint. Let j e {1, 2, -.. , n} with i # j. Calculate S(eijeji) and S(ejieij) respectively. (B) Let i, j e {1,2, -. ,n} with i # j. Let eij e R" be the matrix with 1 on the (i, j)-entry, and 0 everywhere else. Calculate that S(es) = 0. Hint. Calculate S(eijejj) and S(ejjeij) respectively. (C) Let A be anxn matrix such that tr(A) = 0. Use (1) and (2) to conclude S(A) = 0. %3D (D) Use problem 1 to conclude S(X)= tr(X), for all n x n matrix X.
Percentage
A percentage is a number indicated as a fraction of 100. It is a dimensionless number often expressed using the symbol %.
Algebraic Expressions
In mathematics, an algebraic expression consists of constant(s), variable(s), and mathematical operators. It is made up of terms.
Numbers
Numbers are some measures used for counting. They can be compared one with another to know its position in the number line and determine which one is greater or lesser than the other.
Subtraction
Before we begin to understand the subtraction of algebraic expressions, we need to list out a few things that form the basis of algebra.
Addition
Before we begin to understand the addition of algebraic expressions, we need to list out a few things that form the basis of algebra.

![1.
„ Let S, T : R"m → R be linear transformations. Suppose that ker S C ker T.
Show that there exists a fixed scalar a E R such that T(x) = aS(x) for all x E R™.
Hint. Use rank-nullity theorem.
2.
trace.
Let n = 4 (we choose 4 for calculation simplicity, but the following are true for arbitrary n).
Consider the following linear transformation:
tr : Rn?
a11
a12
a13
ain
a21
а22
a23
A2n
n
a31
a32
a33
a3n
Haji + a22+ a33 + · · · + ann =
i=1
anl an2 an3
Ann
(1) .
that tr(In) = n.
Let In be the n x n identity matrix (or equivalently, a vector in Rn). Calculate
(2)
tr(AB) =
Let A, B be two n x n matrices (or equivalently, a vector in Rn). Calculate that
tr(BA).
Hint. Write A = [aij] and B = [bki]. Write down the diagonal of AB and BA in terms of aij
and bki. Then cотрute tr(AB) and tr(BA).](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Facdec92e-028d-4f37-af60-841922a4cee5%2F3f2873f7-77e3-4f49-b77e-714473305eed%2F3ni5y9l_processed.jpeg&w=3840&q=75)

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