use earlier numeric coordinates with u=0

sqrt=sp.sqrt b = 7sqrt(3)/6 h = 5sqrt(3)/6 S = sp.Matrix([0,0,h]) A = sp.Matrix([0,-sp.Rational(3,2),0]) B = sp.Matrix([b,0,0]) C = sp.Matrix([0,sp.Rational(3,2),0]) D = sp.Matrix([-b,0,0]) K = S + sp.Rational(2,5)(B-S) M = S + sp.Rational(1,4)(C-S) N = S + sp.Rational(2,5)*(D-S)

def TV(P1,P2,P3,P4): return abs(sp.Matrix.hstack(P2-P1,P3-P1,P4-P1).det()/6)

V_SABD = TV(S,A,B,D) V_SAKN = TV(S,A,K,N) V_ratio = sp.simplify(V_SAKN/V_SABD) V_SABD, V_SAKN, V_ratio