how to solve tan(2x)=-5x

this question don't have unique value. but using "solve(tan(2*x)+5*x == 0)" then answer is only '0'. how to find another answer?

Answer 1

[John D'Errico]

Using vpasolve instead of solve, you can provide a starting value. Since there will be no analytical solution anyway, when solve realizes that, it will just use vpasolve. But you need to force it to choose a different root with a starting value different from zero.

Or, you could have used fzero instead, which will insist on a starting value, and which prefers a starting bracket that surrounds a root.

Answer 2

[Andrei Bobrov]

example for interval -10*pi:10*pi

f = @(x,w)tan(w*x)+5*x
w = 2; % in your case
x = -10*pi+pi/(2*w):pi/w:10*pi-pi/(2*w);
s = eps(100);
out = arrayfun(@(t,k)fzero(@(x)f(x,w),[t,k]),s+x(1:end-1),x(2:end)-s);