---

function F = primer3(t,y)
c = 7500;          % можно менять
m = 300;
P0 = 10;
k = sqrt(c/m);
P1 = P0/m;
w = 5;             % ω ≈ k или ω = k (k = 5)

F = [y(2);
     -k^2*y(1) + P1*sin(w*t)];
end
[t,y] = ode45(@primer3,[0 40],[0 0]);
plot(t,y(:,1));   % x(t)

function F = primer4(t,y)
c = 7500;
m = 300;
b = 50;
P0 = 10;
k = sqrt(c/m);
n = b/(2*m);
P1 = P0/m;
w = 5;             % ω ≈ k или ω = k

F = [y(2);
     -2*n*y(2) - k^2*y(1) + P1*sin(w*t)];
end

[t,y] = ode45(@primer4,[0 40],[0 0]);
plot(t,y(:,1));   % x(t)