𝑏) 𝑉𝑒̃ 𝑑𝑜̂̀ 𝑡ℎ𝑖̣ (𝑡𝑜̣𝑎 𝑑𝑜̣̂ - 𝑡ℎ𝑜̛̀𝑖 𝑔𝑖𝑎𝑛) 𝑐𝑢̉𝑎 𝟸 𝑥𝑒

𝟷. 𝐷𝑎̣̆𝑡:

* 𝐺𝑜̂́𝑐 𝑡𝑜̣𝑎 𝑑𝑜̣̂: 𝐴
* 𝐺𝑜̂́𝑐 𝑡ℎ𝑜̛̀𝑖 𝑔𝑖𝑎𝑛: 𝑙𝑢́𝑐 𝟸 𝑥𝑒 𝑏𝑎̆́𝑡 𝑑𝑎̂̀𝑢
* 𝐶ℎ𝑖𝑒̂̀𝑢 𝑑𝑢̛𝑜̛𝑛𝑔: 𝑡𝑢̛̀ 𝐴 𝑑𝑒̂́𝑛 𝐵

---

*𝟸. 𝑃ℎ𝑢̛𝑜̛𝑛𝑔 𝑡𝑟𝑖̀𝑛ℎ 𝑡𝑜̣𝑎 𝑑𝑜̣̂ 𝑡ℎ𝑒𝑜 𝑡ℎ𝑜̛̀𝑖 𝑔𝑖𝑎𝑛

𝑋𝑒 𝟷 (𝑣𝟷 = 𝟼𝟶 𝑘𝑚/ℎ):

𝑇𝑢̛̀ 𝟶 → 𝟸ℎ:

```
𝑥𝟷(𝑡) = 𝟼𝟶·𝑡      (𝟶 ≤ 𝑡 ≤ 𝟸)
```

* 𝑇𝑢̛̀ 𝟸ℎ 𝑡𝑟𝑜̛̉ 𝑑𝑖 (𝑑𝑜̂̉𝑖 𝑐ℎ𝑖𝑒̂̀𝑢, 𝑣 = -𝟼𝟶 𝑘𝑚/ℎ):

```
𝑥𝟷(𝑡) = 𝟷𝟸𝟶 - 𝟼𝟶·(𝑡 - 𝟸) = 𝟸𝟺𝟶 - 𝟼𝟶·𝑡   (𝑡 > 𝟸)
```


𝐿𝑢𝑜̂𝑛 𝑑𝑖 𝑡ℎ𝑒𝑜 𝑐ℎ𝑖𝑒̂̀𝑢 𝑑𝑢̛𝑜̛𝑛𝑔:

```
𝑥𝟸(𝑡) = 𝟹𝟶·𝑡     (𝑡 ≥ 𝟶)
```

---
𝟹. 𝐺𝑖𝑎𝑜 𝑑𝑖𝑒̂̉𝑚 (ℎ𝑎𝑖 𝑥𝑒 𝑔𝑎̣̆𝑝 𝑛ℎ𝑎𝑢)

𝐺𝑖𝑎̉𝑖 𝑝ℎ𝑢̛𝑜̛𝑛𝑔 𝑡𝑟𝑖̀𝑛ℎ:

```
𝟸𝟺𝟶 - 𝟼𝟶·𝑡 = 𝟹𝟶·𝑡
=> 𝟸𝟺𝟶 = 𝟿𝟶·𝑡
=> 𝑡 = 𝟾/𝟹 (𝑔𝑖𝑜̛̀) ≈ 𝟸,𝟼𝟽ℎ
```

𝑇𝑜𝑎̣ 𝑑𝑜̣̂ 𝑔𝑎̣̆𝑝 𝑛ℎ𝑎𝑢:

```
𝑥 = 𝟹𝟶·(𝟾/𝟹) = 𝟾𝟶 𝑘𝑚
```

---

𝟺. 𝐷𝑎̣𝑛𝑔 𝑑𝑜̂̀ 𝑡ℎ𝑖̣ 𝑥 - 𝑡

 𝑋𝑒 𝟸: 𝑑𝑢̛𝑜̛̀𝑛𝑔 𝑡ℎ𝑎̆̉𝑛𝑔 𝑞𝑢𝑎 𝑔𝑜̂́𝑐, 𝑑𝑜̂́𝑐 𝑛ℎ𝑒̣ (𝟹𝟶)
𝑋𝑒 𝟷

  𝑇𝑢̛̀ 𝑡 = 𝟶 𝑑𝑒̂́𝑛 𝟸ℎ: 𝑑𝑢̛𝑜̛̀𝑛𝑔 𝑡ℎ𝑎̆̉𝑛𝑔 𝑑𝑜̂́𝑐 𝑙𝑜̛́𝑛 (𝟼𝟶), 𝑑𝑒̂́𝑛 𝑑𝑖𝑒̂̉𝑚 (𝟸; 𝟷𝟸𝟶)
   𝑇𝑢̛̀ 𝑡 > 𝟸ℎ: 𝑑𝑢̛𝑜̛̀𝑛𝑔 𝑡ℎ𝑎̆̉𝑛𝑔 𝑑𝑖 𝑥𝑢𝑜̂́𝑛𝑔 (𝑑𝑜̂́𝑐 -𝟼𝟶), 𝑐𝑎̆́𝑡 𝑑𝑢̛𝑜̛̀𝑛𝑔 𝑐𝑢̉𝑎 𝑥𝑒 𝟸 𝑡𝑎̣𝑖 (𝟾/𝟹; 𝟾𝟶)

𝑏𝑎̣𝑛 𝑐ℎ𝑖̣𝑢 𝑘ℎ𝑜́ 𝑡𝑢̛̣ 𝑣𝑒̃ 𝑏𝑖𝑒̂̉𝑢 𝑑𝑜̂̀ 𝑛ℎ𝑎 

𝑔𝑢̛̉𝑖 𝑐𝑎̣̂𝑢 
    #𝐶𝑎𝑡𝑡𝑢𝑜𝑛𝑔 (𝑥𝑖𝑛 ℎ𝑎𝑦 𝑛ℎ𝑎̂́𝑡 𝑛ℎ𝑎𝑎)