Tìm x, |7 - 2x| = |5 - 3x| + |x + 2| Tham khảo câu trả lời từ Trợ lý ảo Lazi To solve the equation \( |7 - 2x| = |5 - 3x| + |x + 2| \), we need to consider the different cases based on the values of \( x \) that affect the absolute value expressions. ### Step 1: Identify critical points The critical points occur when the expressions inside the absolute values are equal to zero: 1. \( 7 - 2x = 0 \Rightarrow x = \frac{7}{2} = 3.5 \) 2. \( 5 - 3x = 0 \Rightarrow x = \frac{5}{3} \approx 1.67 \) 3. \( x + 2 = 0 \Rightarrow x = -2 \) ### Step 2: Set up intervals The critical points divide the real line into the following intervals: 1. \( (-\infty, -2) \) 2. \( [-2, \frac{5}{3}) \) 3. \( [\frac{5}{3}, \frac{7}{2}) \) 4. \( [\frac{7}{2}, +\infty) \) ### Step 3: Analyze each interval 1. **Interval \( (-\infty, -2) \)**: - Both \( |7 - 2x| = 7 - 2x \) - \( |5 - 3x| = 5 - 3x \) - \( |x + 2| = - (x + 2) = -x - 2 \) The equation becomes: \[ 7 - 2x = (5 - 3x) + (-x - 2) \] Simplifying: \[ 7 - 2x = 5 - 3x - x - 2 \] \[ 7 - 2x = 3 - 4x \] \[ 2x + 4x = 3 - 7 \] \[ 6x = -4 \Rightarrow x = -\frac{2}{3} \quad (\text{not in this interval}) \] 2. **Interval \( [-2, \frac{5}{3}) \)**: - \( |7 - 2x| = 7 - 2x \) - \( |5 - 3x| = 5 - 3x \) - \( |x + 2| = x + 2 \) The equation becomes: \[ 7 - 2x = (5 - 3x) + (x + 2) \] Simplifying: \[ 7 - 2x = 5 - 3x + x + 2 \] \[ 7 - 2x = 7 - 2x \] This holds true for all \( x \) in this interval. 3. **Interval \( [\frac{5}{3}, \frac{7}{2}) \)**: - \( |7 - 2x| = 7 - 2x \) - \( |5 - 3x| = 3x - 5 \) - \( |x + 2| = x + 2 \) The equation becomes: \[ 7 - 2x = (3x - 5) + (x + 2) \] Simplifying: \[ 7 - 2x = 3x - 5 + x + 2 \] \[ 7 - 2x = 4x - 3 \] \[ 7 + 3 = 4x + 2x \] \[ 10 = 6x \Rightarrow x = \frac{5}{3} \quad (\text{in this interval}) \] 4. **Interval \( [\frac{7}{2}, +\infty) \)**: - \( |7 - 2x| = 2x - 7 \) - \( |5 - 3x| = 3x - 5 \) - \( |x + 2| = x + 2 \) The equation becomes: \[ 2x - 7 = (3x - 5) + (x + 2) \] Simplifying: \[ 2x - 7 = 3x - 5 + x + 2 \] \[ 2x - 7 = 4x - 3 \] \[ -7 + 3 = 4x - 2x \] \[ -4 = 2x \Rightarrow x = -2 \quad (\text{not in this interval}) \] ### Conclusion The solution is: \[ \boxed{[-2, \frac{5}{3})} \] And the point \( x = \frac{5}{3} \) is also a valid solution. Therefore, the complete solution set is \( [-2, \frac{5}{3}] \).