9. ถ้า $$ x=-6 $$ แล้วค่าของ $$ x(x-3)(x+4) $$ เท่ากับข้อใด 1. -144 2. -108 3. -72 4. -18 10. กำหนดให้ $$ x=5, y=-4 ; z=-2 $$ แล้ว ค่าของ $$ x y+x z+y z $$ เท่ากับข้อใด 1. -22 2. -18 3. -8 4. 0 11. ผลลัพธ์ของ $$ [(-23) \div 23](-1) $$ เท่ากับจำนวน ใด 1. -23 2. -1 3. 1 4. 23

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Let's solve each problem step by step.

### Problem 9
We need to evaluate $$ x(x-3)(x+4) $$ when $$ x = -6 $$.

1. Substitute $$ x = -6 $$:
   $$
   -6(-6-3)(-6+4)
   $$
2. Calculate each term:
   - $$ -6 - 3 = -9 $$
   - $$ -6 + 4 = -2 $$
3. Now substitute back:
   $$
   -6 \times (-9) \times (-2)
   $$
4. Calculate the product:
   - First, calculate $$ -6 \times -9 = 54 $$
   - Then, $$ 54 \times -2 = -108 $$

Thus, the answer for Problem 9 is **-108**.

### Problem 10
We need to evaluate $$ xy + xz + yz $$ given $$ x = 5, y = -4, z = -2 $$.

1. Substitute the values:
   $$
   5 \times (-4) + 5 \times (-2) + (-4) \times (-2)
   $$
2. Calculate each term:
   - $$ 5 \times -4 = -20 $$
   - $$ 5 \times -2 = -10 $$
   - $$ -4 \times -2 = 8 $$
3. Now sum them up:
   $$
   -20 + (-10) + 8 = -20 - 10 + 8 = -22
   $$

Thus, the answer for Problem 10 is **-22**.

### Problem 11
We need to evaluate $$ [(-23) \div 23](-1) $$.

1. Calculate $$ -23 \div 23 $$:
   $$
   -1
   $$
2. Now multiply by $$-1$$:
   $$
   -1 \times -1 = 1
   $$

Thus, the answer for Problem 11 is **1**.

### Summary of Answers
- Problem 9: **-108**
- Problem 10: **-22**
- Problem 11: **1**
- Problem 9: -108 - Problem 10: -22 - Problem 11: 1

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