Vector Algebra

If the four points, whose position vectors are \(3\widehat i - 4\widehat j + 2\widehat k,\widehat i + 2\widehat j - \widehat k, - 2\widehat i - \widehat j + 3\widehat k\) and \(5\widehat i - 2\alpha \widehat j + 4\widehat k\) are coplanar, then \(\alpha\) is equal to :