In square \(ABCD\), \(A=(-2,1),B=(1,5),C=(a,b)\), where \(a,b\) are both positive integers.

(a) Find the coordinates of \(C,D\). You may use a coordinate grid to help. [4]

(b(i)) For \(P=(-1,3),Q=(6,4)\), find the midpoint of \(PQ\). [2]

(b(ii)) Find \(PQ\). [3]

(b(iii)) Find the gradient of \(PQ\). [2]

(b(iv)) Find the equation of the line parallel to \(PQ\) that meets the \(x\)-axis at \(x=2\). [3]