If p₁ and p₂ are mutually perpendicular principal stresses acting on a soil mass, the normal stress on any plane inclined at angle θ° to the principal plane carrying the principal stress p₁, is:

• A. [(p₁ - p₂)/2] + [(p₁ + p₂)/2] sin 2θ
• B. [(p₁ - p₂)/2] + [(p₁ + p₂)/2] cos 2θ
• C. [(p₁ + p₂)/2] + [(p₁ - p₂)/2] cos 2θ
• D. [(p₁ + p₂)/2] + [(p₁ - p₂)/2] sin 2θ