What is the correct answer?
4
A. (σx + σy)/2 + (1/2) × √[(σx - σy)² + 4 τ²xy]
B. (σx + σy)/2 - (1/2) × √[(σx - σy)² + 4 τ²xy]
C. (σx - σy)/2 + (1/2) × √[(σx + σy)² + 4 τ²xy]
D. (σx - σy)/2 - (1/2) × √[(σx + σy)² + 4 τ²xy]