if not using

EigenvectorSol := simplify(solve({seq(seq((NewMatrix3 . NewInput3(1..-1,i))[j]=(v[i]* NewInput3(1..-1,i))[j], j=1..3), i=1..3)}, {seq(x||i, i=1..9)}));

and if want to see clearly the steps about how to solve for eignvector, how to do?

because i use solve, it has error

InputMatrix3 := Matrix([[31.25,30.8,30.5],[30.8,30.5,0],[30.5,0,0]]);

NewInput3 := MatrixMatrixMultiply(Transpose(InputMatrix3), InputMatrix3);

FirstEigenValue := solve(Determinant(NewInput3-Matrix([[lambda1, 0, 0], [0, lambda1, 0], [0, 0, lambda1]])), lambda1)[1]; # find back eigenvalue from eigenvector

SecondEigenValue := solve(Determinant(NewInput3-Matrix([[lambda1, 0, 0], [0, lambda1, 0], [0, 0, lambda1]])), lambda1)[2]; # find back eigenvalue from eigenvector

ThirdEigenValue := solve(Determinant(NewInput3-Matrix([[lambda1, 0, 0], [0, lambda1, 0], [0, 0, lambda1]])), lambda1)[3]; # find back eigenvalue from eigenvector

v:=[ FirstEigenValue, SecondEigenValue, ThirdEigenValue];

NewMatrix3 := Matrix([[x1,x2,x3], [x4,x5,x6], [x7,x8,x9]]);

EigenvectorSol := simplify(solve({seq(seq((NewMatrix3 . NewInput3(1..-1,i))[j]=(v[i]* NewInput3(1..-1,i))[j], j=1..3), i=1..3)}, {seq(x||i, i=1..9)}));

EigenvectorT := Matrix([[rhs(EigenvectorSol[1]), rhs(EigenvectorSol[2]), rhs(EigenvectorSol[3])],[ rhs(EigenvectorSol[4]), rhs(EigenvectorSol[5]), rhs(EigenvectorSol[6])],[ rhs(EigenvectorSol[7]), rhs(EigenvectorSol[8]), rhs(EigenvectorSol[9])]]);

Old_Asso_eigenvector := Eigenvectors(MatrixMatrixMultiply(Transpose(InputMatrix3), InputMatrix3));

sys1:=MatrixMatrixMultiply(NewInput3-Matrix([[FirstEigenValue, 0, 0], [0, FirstEigenValue, 0], [0, 0, FirstEigenValue]]),Matrix([[x],[y],[z]]));

sys1a := NewInput3-Matrix([[FirstEigenValue, 0, 0], [0, FirstEigenValue, 0], [0, 0, FirstEigenValue]]);

fsolve({sys1[1][1]=0,sys1[2][1]=0,sys1[3][1]=0}, {x,y,z});

solve([sys1[1][1]=0,sys1[2][1]=0,sys1[3][1]=0], [x,y,z]);

solve([sys1[1]=0,sys1[2]=0,sys1[3]=0], [x,y,z]);

> solve([sys1[1] = 0, sys1[2] = 0, sys1[3] = 0], [x, y, z]);

Error, invalid input: solve expects its 1st argument, eqs, to be of type {`and`, `not`, `or`, algebraic, relation(algebraic), ({set, list})({`and`, `not`, `or`, algebraic, relation(algebraic)})}, but received [(Vector[row](1, {(1) = HFloat(2571.1332294000003)*x+HFloat(1901.9)*y+HFloat(953.125)*z})) = 0, (Vector[row](1, {(1) = HFloat(1901.9)*x+HFloat(1594.5707294000001)*y+HFloat(939.4)*z})) = 0, (Vector[row](1, {(1) = HFloat(953.125)*x+HFloat(939.4)*y+HFloat(645.9307294)*z})) = 0]

v1 := <sys1a[1,1] | sys1a[1,2] | sys1a[1,3]>;

v2 := <sys1a[2,1] | sys1a[2,2] | sys1a[2,3]>;

v3 := <sys1a[3,1] | sys1a[3,2] | sys1a[3,3]>;

v1 := <sys1a[1,1] | sys1a[2,1] | sys1a[3,1]>;

v2 := <sys1a[1,2] | sys1a[2,2] | sys1a[3,2]>;

v3 := <sys1a[1,3] | sys1a[2,3] | sys1a[3,3]>;

eigenvector1 := Basis([v1, v2, v2]);

eliminate({sys1[1][1]=0,sys1[2][1]=0,sys1[3][1]=0},{x,y,z});

eliminate({sys1[1][1]=0,sys1[1][2]=0,sys1[1][3]=0},{x,y,z});

sys1:=MatrixMatrixMultiply(NewInput3-Matrix([[SecondEigenValue, 0, 0], [0, SecondEigenValue, 0], [0, 0, SecondEigenValue]]),Matrix([[x],[y],[z]]));

solve([sys1[1][1]=0,sys1[2][1]=0,sys1[3][1]=0], [x,y,z]);

sys1:=MatrixMatrixMultiply(NewInput3-Matrix([[ThirdEigenValue, 0, 0], [0, ThirdEigenValue, 0], [0, 0, ThirdEigenValue]]),Matrix([[x],[y],[z]]));

solve([sys1[1][1]=0,sys1[2][1]=0,sys1[3][1]=0], [x,y,z]);