Given the equation
$$r = B + e(r\cos(\theta))$$
and the corresponding data:
$\theta: 0.88; 1.1; 1.42; 1.77; 2.14$ and $r: 3; 2.4; 1.65; 1.25; 1.01$
How do you input these data for matlab to solve for $B$ and $e$?
Cleve Moler's Numerical Computing with MATLAB has this excellent chapter on how to do least squares; you can adapt any of the methods discussed there. To give you a few nudges on how to do your code: you have
OP seems to have some difficulty seeing how least squares applies here, so here's a hint on how to assemble the equations: