Solve the equation 8−ext11−2x=−x8 - ext{\sqrt{11 - 2x}} = -x, giving your answer in the form a+bca + b\sqrt{c}, where aa, bb and cc are integers.

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Worked solution

4

1. Isolate the surd term on one side of the equation.

8+x=11−2x8 + x = \sqrt{11 - 2x}

2. Square both sides to eliminate the square root and form a quadratic equation.

(8+x)2=11−2x(8 + x)^2 = 11 - 2x
64+16x+x2=11−2x64 + 16x + x^2 = 11 - 2x
x2+18x+53=0x^2 + 18x + 53 = 0

3. Solve the quadratic equation using the quadratic formula.

x=−18±182−4(1)(53)2x = \frac{-18 \pm \sqrt{18^2 - 4(1)(53)}}{2}
x=−18±324−2122x = \frac{-18 \pm \sqrt{324 - 212}}{2}
x=−18±1122x = \frac{-18 \pm \sqrt{112}}{2}

4. Simplify the surd and check for extraneous solutions.

112=16×7=47\sqrt{112} = \sqrt{16 \times 7} = 4\sqrt{7}
x=−18±472=−9±27x = \frac{-18 \pm 4\sqrt{7}}{2} = -9 \pm 2\sqrt{7}

Check the solutions in the original equation (or note that 8+x≥08 + x \ge 0):
If x=−9−27x = -9 - 2\sqrt{7}, 8+x=−1−27<08 + x = -1 - 2\sqrt{7} < 0, which is invalid since a principal square root cannot be negative.
If x=−9+27x = -9 + 2\sqrt{7}, 8+x=−1+27>08 + x = -1 + 2\sqrt{7} > 0, which is valid.

Therefore, x=−9+27x = -9 + 2\sqrt{7}.

Answer

−9+27-9 + 2\sqrt{7}

AI analysis — may contain mistakes.

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