how to subs more than one value in one equation

I want to replace more than one variable in one equation

syms x1 x2 x3;

x1 = (-50+x2+12*x3)/3;

x2 = 6*x1-x3-3;

x3 = 40-6*x1-9*x2;

z = subs(x1,0);

x1 = subs(z,0)

i want to do the last to steps in one step

[darova]

Which variable should be replaced with zero here?

z  = subs(x1,0);

[ali almarzooqi]

I want to replace the two variable at the same time with zero

Answer 1

[darova]

Place variables in square brackets

syms x y z
eqn = x + 2*y + z;
eqn1 = subs(eqn,[x z],[0 0])        % new equation with replaced variables