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Quadratic Equation and Inequalities question

2021 · 25 Jul · Shift 2 · Q35
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  5. /2021 · 25 Jul · Shift 2 · Q35

Quadratic Equation and Inequalities question

2021 · 25 Jul · Shift 2 · Q35

JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
The number of real solutions of the equation, x2 −-−|x|−-− 12 = 0 is :
  1. A
    2
  2. B
    3
  3. C
    1
  4. D
    4
View written solutionFree

Correct answer: A

  1. We need to solve x2−∣x∣−12=0x^2-|x|-12=0x2−∣x∣−12=0 and count the number of real solutions.

  2. Since the equation contains ∣x∣|x|∣x∣, split into cases.

Case 1: x≥0x \ge 0x≥0

Then ∣x∣=x|x|=x∣x∣=x. So the equation becomes x2−x−12=0x^2-x-12=0x2−x−12=0 Factorizing, x2−x−12=(x−4)(x+3)=0x^2-x-12=(x-4)(x+3)=0x2−x−12=(x−4)(x+3)=0 So the roots are x=4, −3x=4,\,-3x=4,−3 But in this case we require x≥0x\ge 0x≥0, so only x=4x=4x=4 is valid.

Case 2: x<0x<0x<0

Then ∣x∣=−x|x|=-x∣x∣=−x. So the equation becomes x2−(−x)−12=0  ⟹  x2+x−12=0x^2-(-x)-12=0 \implies x^2+x-12=0x2−(−x)−12=0⟹x2+x−12=0 Factorizing, x2+x−12=(x+4)(x−3)=0x^2+x-12=(x+4)(x-3)=0x2+x−12=(x+4)(x−3)=0 So the roots are x=−4, 3x=-4,\,3x=−4,3 But in this case we require x<0x<0x<0, so only x=−4x=-4x=−4 is valid.

  1. Therefore, the real solutions are x=4andx=−4x=4 \quad \text{and} \quad x=-4x=4andx=−4 Hence, the number of real solutions is 222

  2. Checking options:

  • A: 222 ✅
  • B: 333 ❌
  • C: 111 ❌
  • D: 444 ❌

So the correct option is A.

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