Finding roots of a hyperbolic function

I have a problem that states when L=4.2m, the function 1+cosh(B*L)cos(B*L)=0 should return 2 positive roots? I have attempted the following, but i am given a negative value. Please help

L=4.2

syms B

eqn=1+cosh(B.*L).*cos(B.*L)==0

solx=solve(eqn,B)

Answer 1

[Walter Roberson]

The cos(B*L) is going to alternate between positive and negative every Pi radians, so every Pi/L in terms of B. The cosh() part just keeps increasing.

Therefore there will be an infinite number of roots, not just 2 roots. You can use vpasolve() passing in search ranges if you need to isolate two particular values.