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## Homework Statement

Find the principal stresses and the orientation for the principal axis of stress for the following cases of plane stress.

σ

_{x}= 4,000 psi

σ

_{y}= 0 psi

τ

_{xy}= 8,000 psi

## Homework Equations

See picture.

## The Attempt at a Solution

https://mail.google.com/mail/u/0/?ui=2&ik=bc68d58ae7&view=att&th=139dbef260c42514&attid=0.1&disp=inline&realattid=f_h79p3pz70&safe=1&zw

I solved this problem using Mohr's Circle. However, the solution to the problem is different and I would like to understand it.

I do not know what the steps mean. Why does the determinate of that function must equal zero?

And what is the n1 and n2 about?

Finally, the 2x2 matrices adds two shear stresses where I was only given one τ

_{xy}where does this other value come from?