Finding roots of a hyperbolic function

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Abraham Robledo
Abraham Robledo 2019-2-28
回答： Walter Roberson 2019-2-28
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)

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回答（1 个）

Walter Roberson
Walter Roberson 2019-2-28
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.

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