If $\overrightarrow{a}=x\hat{i}+(x-1) \hat{j}+\hat{k}$ and $\overrightarrow{\mathit{b}}\mathit{=}\mathit{(}x\mathit{+}\mathit{1}\mathit{)}\widehat{\mathit{ }\mathit{i}}\mathit{+}\mathit{ }\hat{\mathit{j}}\mathit{+}a\hat{\mathit{k}}$  always make an acute angle with each other for every value of $x\in R,$ then