Without using a calculator, solve the inequality xx+2≥22−x\frac{x}{x+2} \ge \frac{2}{2-x}. Hence, solve the inequality ∣x∣∣x∣+2≥22−∣x∣\frac{|x|}{|x|+2} \ge \frac{2}{2-|x|}.

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Worked solution

1(a)

1. Rearrange the inequality to have zero on one side and combine terms into a single fraction.

xx+2−22−x≥0\frac{x}{x+2} - \frac{2}{2-x} \ge 0
x(2−x)−2(x+2)(x+2)(2−x)≥0\frac{x(2-x) - 2(x+2)}{(x+2)(2-x)} \ge 0

2. Expand and simplify the numerator.

2x−x2−2x−44−x2≥0\frac{2x - x^2 - 2x - 4}{4 - x^2} \ge 0
−x2−44−x2≥0\frac{-x^2 - 4}{4 - x^2} \ge 0
Multiply numerator and denominator by −1-1:
x2+4x2−4≥0\frac{x^2 + 4}{x^2 - 4} \ge 0

3. Analyse the signs of the numerator and denominator.

Since x2≥0x^2 \ge 0 for all real xx, the numerator x2+4>0x^2 + 4 > 0.
For the fraction x2+4x2−4\frac{x^2 + 4}{x^2 - 4} to be greater than or equal to 00, the denominator must be strictly positive (since division by zero is undefined):
x2−4>0x^2 - 4 > 0

4. Solve the resulting quadratic inequality to find the range of $x$.

(x−2)(x+2)>0(x-2)(x+2) > 0
x<−2 or x>2x < -2 \text{ or } x > 2

Answer

x<−2 or x>2x < -2 \text{ or } x > 2

1(b)

1. Concisely solve the inequality from part (a) to establish the base result

To use the 'Hence' method, we first determine the solution to part (a):
xx+2−22−x≥0\frac{x}{x+2} - \frac{2}{2-x} \ge 0
x(2−x)−2(x+2)(x+2)(2−x)≥0\frac{x(2-x) - 2(x+2)}{(x+2)(2-x)} \ge 0
−(x2+4)(x+2)(2−x)≥0\frac{-(x^2 + 4)}{(x+2)(2-x)} \ge 0
Since −(x2+4)<0-(x^2 + 4) < 0 for all real xx, the denominator must be strictly negative:
(x+2)(2−x)<0(x+2)(2-x) < 0
(x+2)(x−2)>0(x+2)(x-2) > 0
x<−2orx>2x < -2 \quad \text{or} \quad x > 2

2. Apply the substitution $x \to |x|$ to find the conditions for the target inequality

Replacing xx with ∣x∣|x| in the given inequality perfectly matches the form in part (a).
Hence, applying the result from part (a) by substituting x=∣x∣x = |x|:
∣x∣<−2or∣x∣>2|x| < -2 \quad \text{or} \quad |x| > 2

3. Solve the resulting modulus inequalities, rejecting any invalid cases

Since the absolute value ∣x∣≥0|x| \ge 0 for all real numbers, ∣x∣<−2|x| < -2 has no real solutions.
Solving the second inequality:
∣x∣>2  ⟹  x<−2orx>2|x| > 2 \implies x < -2 \quad \text{or} \quad x > 2

Answer

x < -2 \text{ or } x > 2

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