(x + 1)/(x ^ 2 + x + 1) - (x - 1)/(x ^ 2 - x + 1) = (2 * (x + 2) ^ 2)/(x ^ 6 - 1) (x + 1)/(x ^ 2 + x + 1) - (x - 1)/(x ^ 2 - x + 1) = (2 * (x + 2) ^ 2)/(x ^ 6 - 1)
Tham khảo câu trả lời từ Trợ lý ảo Lazi To solve the equation \[ \frac{x + 1}{x^2 + x + 1} - \frac{x - 1}{x^2 - x + 1} = \frac{2(x + 2)^2}{x^6 - 1}, \] we will start by simplifying each term step by step. ### Step 1: Simplify the Left-Hand Side (LHS) First, let's find a common denominator for the fractions on the LHS: \[ \frac{x + 1}{x^2 + x + 1} - \frac{x - 1}{x^2 - x + 1}. \] The common denominator is \((x^2 + x + 1)(x^2 - x + 1)\). Rewrite each fraction with the common denominator: \[ \frac{(x + 1)(x^2 - x + 1) - (x - 1)(x^2 + x + 1)}{(x^2 + x + 1)(x^2 - x + 1)}. \] Expand the numerators: \[ (x + 1)(x^2 - x + 1) = x^3 - x^2 + x + x^2 - x + 1 = x^3 + 1, \] \[ (x - 1)(x^2 + x + 1) = x^3 + x^2 + x - x^2 - x - 1 = x^3 - 1. \] So the LHS becomes: \[ \frac{x^3 + 1 - (x^3 - 1)}{(x^2 + x + 1)(x^2 - x + 1)} = \frac{x^3 + 1 - x^3 + 1}{(x^2 + x + 1)(x^2 - x + 1)} = \frac{2}{(x^2 + x + 1)(x^2 - x + 1)}. \] ### Step 2: Simplify the Right-Hand Side (RHS) The RHS is: \[ \frac{2(x + 2)^2}{x^6 - 1}. \] Notice that \(x^6 - 1\) can be factored as: \[ x^6 - 1 = (x^3 - 1)(x^3 + 1). \] Thus, the RHS becomes: \[ \frac{2(x + 2)^2}{(x^3 - 1)(x^3 + 1)}. \] ### Step 3: Compare LHS and RHS We need to compare: \[ \frac{2}{(x^2 + x + 1)(x^2 - x + 1)} \] with \[ \frac{2(x + 2)^2}{(x^3 - 1)(x^3 + 1)}. \] Recall that: \[ x^3 - 1 = (x - 1)(x^2 + x + 1) \] and \[ x^3 + 1 = (x + 1)(x^2 - x + 1). \] Thus, \[ (x^3 - 1)(x^3 + 1) = (x - 1)(x^2 + x + 1)(x + 1)(x^2 - x + 1). \] So, \[ \frac{2}{(x^2 + x + 1)(x^2 - x + 1)} = \frac{2}{(x^2 + x + 1)(x^2 - x + 1)}. \] This implies that: \[ (x + 2)^2 = 1. \] Solving for \(x\): \[ x + 2 = \pm 1. \] Thus, \[ x + 2 = 1 \implies x = -1, \] or \[ x + 2 = -1 \implies x = -3. \] ### Step 4: Verify Solutions We need to check if \(x = -1\) and \(x = -3\) satisfy the original equation. #### For \(x = -1\): LHS: \[ \frac{-1 + 1}{(-1)^2 - 1 + 1} - \frac{-1 - 1}{(-1)^2 + 1 + 1} = \frac{0}{1} - \frac{-2}{3} = 0 + \frac{2}{3} = \frac{2}{3}. \] RHS: \[ \frac{2(-1 + 2)^2}{(-1)^6 - 1} = \frac{2(1)^2}{1 - 1} = \frac{2}{0}, \] which is undefined. So, \(x = -1\) is not a valid solution. #### For \(x = -3\): LHS: \[ \frac{-3 + 1}{(-3)^2 - 3 + 1} - \frac{-3 - 1}{(-3)^2 + 3 + 1} = \frac{-2}{9 - 3 + 1} - \frac{-4}{9 + 3 + 1} = \frac{-2}{7} + \frac{4}{13}. \] RHS: \[ \frac{2(-3 + 2)^2}{(-3)^6 - 1} = \frac{2(-1)^2}{729 - 1} = \frac{2}{728} = \frac{1}{364}. \] Since \(\frac{-2}{7} + \frac{4}{13} \neq \frac{1}{364}\), \(x = -3\) is not a valid solution either. Thus, the equation has no valid solutions.