Issues with subs function

Hi, I'm doing some stuff with structural analysis and I need to substitute a symbolic variable in a symbolic funtion, but it seems that matlab substitutes all the variables when i need just to change one of them, then, the resulting expression must have one of the variables, but that does not happen ¿Could someone help me please?

l1=3;
h1=1.45;
b1=sqrt(l1^2+h1^2);
z=atand(h1/l1);
q1 = 0;

syms r1v x

R2v(r1v) =r1v/3 - 209/1395;

Mz1v(r1v,x) = -r1v + (R2v(r1v) * cosd(z)) * x + (q1 * sind(z)) * x

Mz1v(r1v, x) = 

subs(Mz1v,x,b1)

ans(r1v, x) = 

The expected ouput should have an expression in terms of r1v because i'm just changing the value of x but it does not happen

Answer 1

[Paul]

I'm sure if you go through it step-by-step, or w/o assigning numbers until the end, you'll see that value of b1 is magical and all of the terms in r1v go away

l1=3;
h1=1.45;
syms l1 h1 real
b1=sqrt(l1^2+h1^2);
z=atand(h1/l1);
q1 = 0;
syms r1v x
R2v(r1v) =r1v/3 - 209/1395;
Mz1v(r1v,x) = -r1v + (R2v(r1v) * cosd(z)) * x + (q1 * sind(z)) * x

Mz1v(r1v, x) = 

Mz1v = simplify(Mz1v)

Mz1v(r1v, x) = 

Mz1v(r1v,b1)

ans = 

If l1 = 3, as in this case, then the r1v is annihilated, and we're left with

subs(ans,l1,3)

ans =