
Strain Gauge Mechanics
I have some strain gauge calculations to complete to produce a mohrcoloumn circle for rock mechanics, but I seem to be missing a trick with completing the initial calculations.
To be honest, the application probably doesn't matter as the bit I'm stuck on is more a rearrangement of equations.
Q is the radius of the circle which is what I am trying to find, along with E1 and E2 to produce the circle.
The example I have runs through as follows:
Q.Cos 2θ = 363
Q.Sin 2θ = 90.64
Q2 = Q2.Sin2 2θ+ Q2Cos2 2θ = 131769+8215.61
Q = 374.15
The 2's in green are to represent squared symbols as I can't produce an elevated 2 in the message composition box.
I have calculated Q.Cos 2θ and Q.Sin 2θ for my problem, but can't figure out how to get Q2.Sin2 2θ+ Q2Cos2 2θ as eveything is squared apart from 2θ. Am I missing something obvious?!
All help would be greatly appreciated.

I found a way of solving the above using the following, but I still don't get how the example sorts things through.
tan2θ = 0.249
2θ = tan1 0.249 = 13.98
θ = 7
Q.cos13.98 = 363
Q.0.970 = 363
Q= 374.2