1. Isolate the surd term on one side of the equation.
8 + x = 11 − 2 x 8 + x = \sqrt{11 - 2x} 8 + x = 11 − 2 x
2. Square both sides to eliminate the square root and form a quadratic equation.
( 8 + x ) 2 = 11 − 2 x (8 + x)^2 = 11 - 2x ( 8 + x ) 2 = 11 − 2 x
64 + 16 x + x 2 = 11 − 2 x 64 + 16x + x^2 = 11 - 2x 64 + 16 x + x 2 = 11 − 2 x
x 2 + 18 x + 53 = 0 x^2 + 18x + 53 = 0 x 2 + 18 x + 53 = 0
3. Solve the quadratic equation using the quadratic formula.
x = − 18 ± 18 2 − 4 ( 1 ) ( 53 ) 2 x = \frac{-18 \pm \sqrt{18^2 - 4(1)(53)}}{2} x = 2 − 18 ± 1 8 2 − 4 ( 1 ) ( 53 )
x = − 18 ± 324 − 212 2 x = \frac{-18 \pm \sqrt{324 - 212}}{2} x = 2 − 18 ± 324 − 212
x = − 18 ± 112 2 x = \frac{-18 \pm \sqrt{112}}{2} x = 2 − 18 ± 112
4. Simplify the surd and check for extraneous solutions.
112 = 16 × 7 = 4 7 \sqrt{112} = \sqrt{16 \times 7} = 4\sqrt{7} 112 = 16 × 7 = 4 7
x = − 18 ± 4 7 2 = − 9 ± 2 7 x = \frac{-18 \pm 4\sqrt{7}}{2} = -9 \pm 2\sqrt{7} x = 2 − 18 ± 4 7 = − 9 ± 2 7
Check the solutions in the original equation (or note that 8 + x ≥ 0 8 + x \ge 0 8 + x ≥ 0 ):
If x = − 9 − 2 7 x = -9 - 2\sqrt{7} x = − 9 − 2 7 , 8 + x = − 1 − 2 7 < 0 8 + x = -1 - 2\sqrt{7} < 0 8 + x = − 1 − 2 7 < 0 , which is invalid since a principal square root cannot be negative.
If x = − 9 + 2 7 x = -9 + 2\sqrt{7} x = − 9 + 2 7 , 8 + x = − 1 + 2 7 > 0 8 + x = -1 + 2\sqrt{7} > 0 8 + x = − 1 + 2 7 > 0 , which is valid.
Therefore, x = − 9 + 2 7 x = -9 + 2\sqrt{7} x = − 9 + 2 7 .
答案 − 9 + 2 7 -9 + 2\sqrt{7} − 9 + 2 7