centre = x + y / 2
raidus or Tao max = sqrt((x-centre)^2 + Tao xy^2)
stress1 = centre + radius (on right side)
stress2 = centre - radius (on left side)
2theta = tan^-1(Tao xy / (stressx - centre))
- rearrange for theta
- draw new diagram of box and stresses
2alpha = 90 - 2theta
- rearrange for alpha