## Precalculus (6th Edition) Blitzer

$-\frac{1}{\sqrt{5}}\mathbf{i}-+\frac{2}{\sqrt{5}}\mathbf{j}$
Unit vector: For any vector $\mathbf{v}$, $\frac{\mathbf{v}}{\left\| \mathbf{v} \right\|}$ is the unit vector in the same direction as the vector $\mathbf{v}$. Magnitude of vector is given by: The magnitude of $\mathbf{v}=a\mathbf{i}+b\mathbf{j}$ is given by $\left\| \mathbf{v} \right\|=\sqrt{{{a}^{2}}+{{b}^{2}}}$. Scalar multiplication of a vector is given by: For any vector $\mathbf{v}=a\mathbf{i}+b\mathbf{j}$ and $k$ is a real number, $k\mathbf{v}=\left( ka \right)\mathbf{i}+\left( kb \right)\mathbf{j}$. Here, $\mathbf{v}=-\mathbf{i}+2\mathbf{j}$. So, \begin{align} & \left\| \mathbf{v} \right\|=\sqrt{{{\left( -1 \right)}^{2}}+{{2}^{2}}} \\ & =\sqrt{1+4} \\ & =\sqrt{5} \end{align} The unit vector in the direction as the vector $\mathbf{v}$ is calculated as below: \begin{align} & \frac{\mathbf{v}}{\left\| \mathbf{v} \right\|}=\frac{-\mathbf{i}+2\mathbf{j}}{\sqrt{5}} \\ & =-\frac{1}{\sqrt{5}}\mathbf{i}-+\frac{2}{\sqrt{5}}\mathbf{j} \end{align} Hence, the unit vector in the direction as the vector $\mathbf{v}$ is $-\frac{1}{\sqrt{5}}\mathbf{i}-+\frac{2}{\sqrt{5}}\mathbf{j}$.