If&nbsp;<span class="math-tex">\(\vec a = \hat i - \hat k,\; \vec b = x\hat i + \hat j + (1 - x)\hat k\)</span>&nbsp;and&nbsp;<span class="math-tex">\(c = y\hat i + x\hat j + (1 + x - y)\hat k,\)</span>&nbsp;then&nbsp;<span class="math-tex">\(\left[\vec a \vec b \vec c\right]\)</span>&nbsp;depends on