With Symbolic Toolbox:
syms t positive
g=9.807; %m/s2
d= 1.225; %kg/m3
A=1.9;
m=84;
Cd=1.14;
fun = 2*m/(A*Cd*d)* log(abs(cosh(t*sqrt(A*Cd*d*g/(2*m)))))-1000 == 0
sol = double(solve(fun,t))
Using basic functions:
g=9.807; %m/s2
d= 1.225; %kg/m3
A=1.9;
m=84;
Cd=1.14;
fun = @(t) 2*m/(A*Cd*d)* log(abs(cosh(t*sqrt(A*Cd*d*g/(2*m)))))-1000
sol = fzero(fun,10)
