Solving an Equation for Different Values of Constants

I am solving a simple equation for x which has constants a b and c. a and b are matrices and c is a constant value. I want 4 values of x for 4 values of a and b. How can I do that? I have written the following code but it doesnt work.

>> a=[2 1 2 3];

>> b=[6 7 8 89];

>> c=123;

>> syms x positive

>> eqn=x^2*a*c-x*b*c+20;

>> y=solve(eqn,x)

This code doesn't work The code works for one value of a and b. For example

>> eqn=x^2*a(1)*c-x*b(1)*c+20;

>> y=solve(eqn,x)

This way it gives one answer. But I want 4 answers for x.

Answer 1

[Walter Roberson]

f = 25;
A = 1000;
b = 200;
d = 450;
B = 0.85;
E = 200000;
e = linspace(0,0.003,15);
s = (f*(2*(e/0.002)-(e/0.002).^2));
syms a positive
v = sym(zeros(length(e),1));

for i = 1:length(e)
  eqn = (a^2)*(s(i)*b)+((a*e(i)*A*E)-(e(i)*B*E*A*d));
  temp = vpasolve(eqn,a);
  temp2 = temp(temp>0);
  if isempty(temp2)
    fprintf('Warning: eqn has no positive solutions for i = %d, and has %d negative solutions\n', i, length(temp));
    v(i) = nan;
  elseif length(temp2) > 1
    fprintf('Warning: eqn has %d positive solutions for i = %d, first is selected\n', length(temp2) );
    v(i) = temp2(1);
  else
    v(i) = temp2;
  end
end
disp(v)

[Iqbal Farjad]

Thanks alot. :)