If P₁ and P² Are Mutually Perpendicular Principal Stresses Acting

Multiple Choice

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

A) (p₁ ? p²) /2+ (p₁ + p²) /2 sin 2?
B) (p₁ ? p²) /2+ (p₁ + p²) /2 cos 2?
C) (p₁ + p²) /2+ (p₁ ? p²) /2 cos 2?
D) (p₁ + p²) /2+ (p₁ ? p²) /2 sin 2?