1. **Simplify the expression** $x^2 - 4 + x(x + 2)$. Start by expanding the term $x(x + 2)$: $$x(x + 2) = x^2 + 2x$$ Now substitute back: $$x^2 - 4 + x^2 + 2x$$ Combine like terms: $$x^2 + x^2 + 2x - 4 = 2x^2 + 2x - 4$$ 2. **Simplify the expression** $x^2 - 4x + 4$. Recognize this as a perfect square trinomial: $$x^2 - 4x + 4 = (x - 2)^2$$ 3. **Exercise ②: Calculate the percentage of girls in the class.** Given: Total students = 30, Girls = 14. Use the formula for percentage: $$\text{Percentage} = \left(\frac{\text{Part}}{\text{Whole}}\right) \times 100$$ Calculate: $$\frac{14}{30} \times 100 = \frac{14 \times 100}{30} = \frac{1400}{30} = 46.67\%$$ So, girls represent 46.67% of the class. 4. **Exercise ③: Price increase problem.** Given: Original price = 500, Increase = 30%. 1) Calculate the amount of increase: $$\text{Increase amount} = \frac{30}{100} \times 500 = 0.3 \times 500 = 150$$ 2) Calculate the new price: $$\text{New price} = \text{Original price} + \text{Increase amount} = 500 + 150 = 650$$ **Final answers:** - Simplified expression 1: $2x^2 + 2x - 4$ - Simplified expression 2: $(x - 2)^2$ - Percentage of girls: 46.67% - Increase amount: 150 - New price: 650