Here is a solution:
% Step 1. Solve for the unknowns of the helix equations using the given P2 point
P1 = [0,0,0];
P2 = [1,3,-5];
% The unknowns: x = r*cos(t), y=r*sin(t), z=c*t.
syms r c t
Eq1 = 1==r*cos(t);
Eq2 = 3==r*sin(t);
Eq3 = -5==c*t;
Sol = solve(Eq1, Eq2, Eq3);
% Solutions
c = double(Sol.c)
r=double(Sol.r)
t=double(Sol.t)
% Step 2. Plot the helix taking a second solution
time = linspace(0, t(2), 200);
R = r(2);
C = c(2);
X = R*sin(time);
Y = R*sin(time);
Z = C*time;
plot3(X,Y,Z, 'ro-', 'markerfacecolor', 'y'), grid on
xlabel('x(t)'), ylabel('y(t)'), zlabel('z(t)')
axis tight
