Parallelogram Vectors
1. **Problem statement:**
We have a parallelogram WXYZ with vectors \(\overrightarrow{WX} = \mathbf{u}\) and \(\overrightarrow{WZ} = \mathbf{v}\). M is the midpoint of \(\overrightarrow{WY}\).
We need to express the following vectors in terms of \(\mathbf{u}\) and \(\mathbf{v}\):
(i) \(\overrightarrow{WY}\), (ii) \(\overrightarrow{WM}\), (iii) \(\overrightarrow{XW}\), (iv) \(\overrightarrow{XZ}\).
Then, show that M is the midpoint of \(\overrightarrow{XZ}\) using vectors.
2. **Recall properties of parallelograms and vectors:**
- In a parallelogram, opposite sides are equal and parallel.
- Vector addition rule: \(\overrightarrow{AB} + \overrightarrow{BC} = \overrightarrow{AC}\).
- Midpoint M of segment WY means \(\overrightarrow{WM} = \frac{1}{2} \overrightarrow{WY}\).
3. **Find each vector:**
(i) \(\overrightarrow{WY}\):
Since WXYZ is a parallelogram, \(\overrightarrow{WY} = \overrightarrow{WX} + \overrightarrow{XY}\).
But \(\overrightarrow{XY} = \overrightarrow{WZ} = \mathbf{v}\) (opposite sides equal), so
$$\overrightarrow{WY} = \mathbf{u} + \mathbf{v}.$$
(ii) \(\overrightarrow{WM}\):
M is midpoint of WY, so
$$\overrightarrow{WM} = \frac{1}{2} \overrightarrow{WY} = \frac{1}{2} (\mathbf{u} + \mathbf{v}).$$
(iii) \(\overrightarrow{XW}\):
This is the vector from X to W, the opposite direction of \(\overrightarrow{WX}\), so
$$\overrightarrow{XW} = -\mathbf{u}.$$
(iv) \(\overrightarrow{XZ}\):
We can write \(\overrightarrow{XZ} = \overrightarrow{XW} + \overrightarrow{WZ} = -\mathbf{u} + \mathbf{v}.$$
4. **Show M is midpoint of XZ:**
We want to show that \(\overrightarrow{XM} = \frac{1}{2} \overrightarrow{XZ}\).
Calculate \(\overrightarrow{XM}\):
$$\overrightarrow{XM} = \overrightarrow{XW} + \overrightarrow{WM} = -\mathbf{u} + \frac{1}{2} (\mathbf{u} + \mathbf{v}) = -\mathbf{u} + \frac{1}{2} \mathbf{u} + \frac{1}{2} \mathbf{v} = -\frac{1}{2} \mathbf{u} + \frac{1}{2} \mathbf{v} = \frac{1}{2} (-\mathbf{u} + \mathbf{v}).$$
Recall from (iv) that \(\overrightarrow{XZ} = -\mathbf{u} + \mathbf{v}\), so
$$\overrightarrow{XM} = \frac{1}{2} \overrightarrow{XZ}.$$
This confirms M is the midpoint of XZ.
**Final answers:**
(i) \(\overrightarrow{WY} = \mathbf{u} + \mathbf{v}\)
(ii) \(\overrightarrow{WM} = \frac{1}{2} (\mathbf{u} + \mathbf{v})\)
(iii) \(\overrightarrow{XW} = -\mathbf{u}\)
(iv) \(\overrightarrow{XZ} = -\mathbf{u} + \mathbf{v}\)
M is the midpoint of XZ because \(\overrightarrow{XM} = \frac{1}{2} \overrightarrow{XZ}\).