# How to find strain in an inclined member of a struss

I'm working through an FEA problem and I'm stuck.

Question: How can I determine the strain in member 3 from displacements known at node 3?

It's at 45 degrees, I know I should be using some $cos\phi$ and $sin\phi$, and given the displacements I suspect there to be a negative strain (indicating compression), however, I'm not entirely sure how to find the strain in the inclined member using both displacements.