BCNN stands for "Bội Chung Nhỏ Nhất" in Vietnamese, which translates to "Least Common Multiple" (LCM) in English. To find the LCM of a set of numbers, you need to determine the smallest number that is a multiple of each of the numbers in the set.

Let's calculate the LCM for each set of numbers:

### BCNN (45, 75, 120)
1. **Prime factorization:**
- 45 = 3² × 5
- 75 = 3 × 5²
- 120 = 2³ × 3 × 5

2. **Take the highest power of each prime number:**
- 2³ (from 120)
- 3² (from 45)
- 5² (from 75)

3. **Multiply these together:**
- LCM = 2³ × 3² × 5² = 8 × 9 × 25 = 1800

So, BCNN (45, 75, 120) = 1800.

### BCNN (56, 24, 72)
1. **Prime factorization:**
- 56 = 2³ × 7
- 24 = 2³ × 3
- 72 = 2³ × 3²

2. **Take the highest power of each prime number:**
- 2³ (common in all)
- 3² (from 72)
- 7 (from 56)

3. **Multiply these together:**
- LCM = 2³ × 3² × 7 = 8 × 9 × 7 = 504

So, BCNN (56, 24, 72) = 504.

### BCNN (50, 75, 125)
1. **Prime factorization:**
- 50 = 2 × 5²
- 75 = 3 × 5²
- 125 = 5³

2. **Take the highest power of each prime number:**
- 2 (from 50)
- 3 (from 75)
- 5³ (from 125)

3. **Multiply these together:**
- LCM = 2 × 3 × 5³ = 2 × 3 × 125 = 750

So, BCNN (50, 75, 125) = 750.

In summary:
- BCNN (45, 75, 120) = 1800
- BCNN (56, 24, 72) = 504
- BCNN (50, 75, 125) = 750