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# How to Pursue Mathematics after High School?

For Students who are passionate for Mathematics and want to pursue it for higher studies in India and abroad.

This is a very beautiful sample problem from ISI MStat PSB 2010 Problem 1 based on Matrix multiplication and Eigen values and Eigen vectors . Let's give it a try !!

## Problem- ISI MStat PSB 2010 Problem 1

Let $A$ be a $4 \times 4$ matrix with non-negative entries such that the sum of the entries in each row of $A$ equals 1 . Find the sum of all entries in matrix $A^{5}$ .

### Prerequisites

Matrix Multiplication

Eigen Values

Eigen Vectors

## Solution :

Doing this problem you have to use the hint given in the question . Here the hint is that the sum of the entries in each row of $A$ equals 1 . How can you use that ? Think about it!

Here comes the trick .

Let V be a vector such that $V={[1,1,1,1]}^{T}$ . Now if we multiply A by V then we will get V i.e $AV=V$ .

This is because it is given that the sum of the entries in each row of $A$ equals 1 .

So, from $AV=V$ we can say that 1 is an eigen value of A .

Hence $A^5V=A^4(AV)=A^4V=A^3(AV)= \cdots = V$ . From here we can say the sum of all the entries of each rows of $A^5$ is 1.

Therefore the sum of all the entries of $A^5$ is also 4 .

## Food For Thought

Let $A$ and B be $n \times n$ matrices with real entries satisfying $tr(A A^{T}+B B^{T})=tr(A B+A^{T} B^{T})$ .
Prove that $A=B^{T}$ .

Hint : Use properties of trace that's the trick here .

## What to do to shape your Career in Mathematics after 12th?

From the video below, let's learn from Dr. Ashani Dasgupta (a Ph.D. in Mathematics from the University of Milwaukee-Wisconsin and Founder-Faculty of Cheenta) how you can shape your career in Mathematics and pursue it after 12th in India and Abroad. These are some of the key questions that we are discussing here:

• What are some of the best colleges for Mathematics that you can aim to apply for after high school?
• How can you strategically opt for less known colleges and prepare yourself for the best universities in India or Abroad for your Masters or Ph.D. Programs?
• What are the best universities for MS, MMath, and Ph.D. Programs in India?
• What topics in Mathematics are really needed to crack some great Masters or Ph.D. level entrances?
• How can you pursue a Ph.D. in Mathematics outside India?
• What are the 5 ways Cheenta can help you to pursue Higher Mathematics in India and abroad?

## Want to Explore Advanced Mathematics at Cheenta?

Cheenta has taken an initiative of helping College and High School Passout Students with its "Open Seminars" and "Open for all Math Camps". These events are extremely useful for students who are really passionate for Mathematic and want to pursue their career in it.

To Explore and Experience Advanced Mathematics at Cheenta

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