已知向量 $\mathit{a}\mathit{b}$夹角为 ${45}^o$^ ，且 $\left|\stackrel{\mathbf{\rightharpoonup }}{\mathbf{a}}\right|=1,\left|2\stackrel{\mathbf{\rightharpoonup }}{\mathbf{a}}-\stackrel{\mathbf{\rightharpoonup }}{\mathbf{b}}\right|=\sqrt{10}$；则 $\stackrel{\mathbf{\rightharpoonup }}{\left|\mathbf{b}\right|}=$.