Let a vertical tower AB of height 2h stands on a horizontal ground. Let from a point P on the ground a man can see up to height h of the tower with an angle of elevation 2α.When from P, he moves a distance d in the direction of \(\overrightarrow{AP}\).he can see the top B of the tower with an angle of elevation α. if \(d = \sqrt7\) h, then tan α is equal to