Number of Solutions of Absolute Equation

CAT 2019 Slot 1 · Quantitative Ability · Medium · Quadratic equations

The number of solutions of the equation ∣x∣(6x2+1)=5x2|x|(6x^2 + 1) = 5x^2 is

Answer

5

Explanation

x=0x = 0 is a solution. For x≠0x \ne 0, divide by x2x^2: ∣x∣(6x2+1)x2=5  ⟹  6x2+1∣x∣=5\frac{|x|(6x^2+1)}{x^2} = 5 \implies \frac{6x^2+1}{|x|} = 5. Let t=∣x∣>0t = |x| > 0. 6t2+1t=5  ⟹  6t2−5t+1=0  ⟹  (2t−1)(3t−1)=0\frac{6t^2 + 1}{t} = 5 \implies 6t^2 - 5t + 1 = 0 \implies (2t - 1)(3t - 1) = 0. t=1/2t = 1/2 or t=1/3t = 1/3. Since t=∣x∣t = |x|, x=±1/2x = \pm 1/2 and x=±1/3x = \pm 1/3. Total solutions =1+2+2=5= 1 + 2 + 2 = 5.

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