c = a * b;

Now if i want to find matrix b means....

b = c * (1/a) = c * inv(a);

Here inv(c) will not work coz it is not a square matrix. Please help me in finding it.

NOTE : PseudoInverse - pinv() in MATLAB is also not working.[/QUOTE]

A non-square matrix does NOT have an inverse, of course. Your matrix a, above, maps R^{3}into R^{2}so obviously, its null space is non-trivial. In this case, its null space is the one dimensional subspace spanned by <1, -2, 1>. That also means that, given a two by two matrix c, there exist an infinite number of two by three matrices, b, such that ab= c.