Find the value of the sum in the expression

[Amelia_T]

Consider the matrix below. Calculate the expression using Excel. What is the value of the sum of the diagonal elements? a11 + a22.

Eqn001.gif


Could somebody help me with this question please?

[Vikas_Gautam]

Hi,
Welcome to this forum...
Try using Matrix Multiplication...

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However you can also use ranges instead of array..

It will return an 2 x 2 array..
{3,-13;3,-7}

if you want to sum it ... then use

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will return -14

[Amelia_T]

Thank you, Vikas_Gautam! You helped me a lot! I had no idea what function could use! Thanks!

[Vikas_Gautam]

You are always welcome..

[Amelia_T]

I have one more doubt, if I change the order of values: = sum (MMULT ({7.1, 4.1}, {0, -2, 3.1})) as you had done , and put in order of the image: =sum(MMULT({7.4, 1.1},{0, -2, 3.1})), resulting in 4 and not -14. Is this wrong? I mean, this change in the order of numbers influences in diagonal sum of the elements?

[Vikas_Gautam]

Amelia..
Actually what I suggested you is as good as multiply to Matrices as we normally do..
Changing the elements' position in the matrix will obviously change the result..

I more thing I wanna clear is that Excel uses ";" to differentiate the ROWS and "," to differentiate the COLUMNS.. (without Quotes..)

However you can also use the ranges instead of Arrays...
try the attached file..

[Amelia_T]

Yes, I understood what you said now. Thank you again for the reply and also for the file! You helped me a lot!

[Vikas_Gautam]

You are always welcome...