` \sqrt{2 + x} = 3 - 2\sqrt{2 - x} `
` <=> 2 + x = 9 - 12\sqrt{2 - x} + 8 - 4x `
` <=> 2 + x = 17 - 12\sqrt{2 - x} - 4x `
` <=> 12\sqrt{2 - x} + 2 + x = 17 - 4x `
` <=> 12\sqrt{2 - x} = 15 - 5x `
` <=> 144(2 - x) = 225 - 150x + 25x^2 `
` <=> 288 - 144x = 225 - 150x + 25x^2 `
` <=> 288 - 144x - 225 + 150 - 25x^2 = 0 `
` <=> -25x^2 + 6x + 63 = 0 `
` <=> -(25x^2 - 6x - 63) = 0 `
` <=> 25x^2 - 6x - 63 = 0 `
` <=> x = \frac{-(-6) ± \sqrt{(-6)^{2}-4.25.(-63)}}{2.25} `
` <=> x = \frac{6 ± 24\sqrt{11}}{50} ` (loại trừ trường hợp âm)
` <=> x = \frac{6 + 24\sqrt{11}}{50} `
` <=> x = \frac{3 + 12\sqrt{11}}{25} `
