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Quadratic Equation and Inequalities question

2025 · 24 Jan · Shift 2 · Q43
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  5. /2025 · 24 Jan · Shift 2 · Q43

Quadratic Equation and Inequalities question

2025 · 24 Jan · Shift 2 · Q43

JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
The number of real solution(s) of the equation x2+3x+2=min⁡{∣x−3∣,∣x+2∣}x^2+3 x+2=\min \{|x-3|,|x+2|\}x2+3x+2=min{∣x−3∣,∣x+2∣} is :
  1. A
    2
  2. B
    3
  3. C
    1
  4. D
    0
View written solutionFree

Correct answer: A

  1. We need to solve x2+3x+2=min⁡{∣x−3∣,∣x+2∣}.x^2+3x+2=\min\{|x-3|,|x+2|\}.x2+3x+2=min{∣x−3∣,∣x+2∣}.

First factor the quadratic: x2+3x+2=(x+1)(x+2).x^2+3x+2=(x+1)(x+2).x2+3x+2=(x+1)(x+2).

So the equation becomes (x+1)(x+2)=min⁡{∣x−3∣,∣x+2∣}.(x+1)(x+2)=\min\{|x-3|,|x+2|\}.(x+1)(x+2)=min{∣x−3∣,∣x+2∣}.

  1. Now determine the function min⁡{∣x−3∣,∣x+2∣}.\min\{|x-3|,|x+2|\}.min{∣x−3∣,∣x+2∣}. This is the smaller of the distances of xxx from 333 and from −2-2−2.

The midpoint of 333 and −2-2−2 is 3+(−2)2=12.\frac{3+(-2)}{2}=\frac12.23+(−2)​=21​. So:

  • if x≤12x\le \frac12x≤21​, then xxx is closer to −2-2−2, hence min⁡{∣x−3∣,∣x+2∣}=∣x+2∣;\min\{|x-3|,|x+2|\}=|x+2|;min{∣x−3∣,∣x+2∣}=∣x+2∣;
  • if x≥12x\ge \frac12x≥21​, then xxx is closer to 333, hence min⁡{∣x−3∣,∣x+2∣}=∣x−3∣.\min\{|x-3|,|x+2|\}=|x-3|.min{∣x−3∣,∣x+2∣}=∣x−3∣.

Thus solve piecewise.


  1. Case I: x≤12x\le \frac12x≤21​

Then the equation is x2+3x+2=∣x+2∣.x^2+3x+2=|x+2|.x2+3x+2=∣x+2∣. Now split again based on sign of x+2x+2x+2.

Case I(a): x≤−2x\le -2x≤−2

Then ∣x+2∣=−(x+2)|x+2|=-(x+2)∣x+2∣=−(x+2), so x2+3x+2=−x−2x^2+3x+2=-x-2x2+3x+2=−x−2 x2+4x+4=0x^2+4x+4=0x2+4x+4=0 (x+2)2=0(x+2)^2=0(x+2)2=0 x=−2.x=-2.x=−2. This satisfies x≤−2x\le -2x≤−2, so it is a valid solution.

Case I(b): −2≤x≤12-2\le x\le \frac12−2≤x≤21​

Then ∣x+2∣=x+2|x+2|=x+2∣x+2∣=x+2, so x2+3x+2=x+2x^2+3x+2=x+2x2+3x+2=x+2 x2+2x=0x^2+2x=0x2+2x=0 x(x+2)=0x(x+2)=0x(x+2)=0 x=0orx=−2.x=0\quad \text{or}\quad x=-2.x=0orx=−2. Both satisfy −2≤x≤12-2\le x\le \frac12−2≤x≤21​, so both are valid.

So from Case I, solutions are x=−2,  0.x=-2,\;0.x=−2,0.


  1. Case II: x≥12x\ge \frac12x≥21​

Then the equation is x2+3x+2=∣x−3∣.x^2+3x+2=|x-3|.x2+3x+2=∣x−3∣. Again split by sign of x−3x-3x−3.

Case II(a): 12≤x≤3\frac12\le x\le 321​≤x≤3

Then ∣x−3∣=3−x|x-3|=3-x∣x−3∣=3−x, so x2+3x+2=3−xx^2+3x+2=3-xx2+3x+2=3−x x2+4x−1=0.x^2+4x-1=0.x2+4x−1=0. Solving, x=−4±16+42=−4±202=−2±5.x=\frac{-4\pm\sqrt{16+4}}{2}=\frac{-4\pm\sqrt{20}}{2}=-2\pm\sqrt5.x=2−4±16+4​​=2−4±20​​=−2±5​. Now check interval [12,3]\left[\frac12,3\right][21​,3]:

  • −2−5<0-2-\sqrt5<0−2−5​<0, invalid
  • −2+5≈0.236<12-2+\sqrt5\approx 0.236<\frac12−2+5​≈0.236<21​, invalid

So no solution from this subcase.

Case II(b): x≥3x\ge 3x≥3

Then ∣x−3∣=x−3|x-3|=x-3∣x−3∣=x−3, so x2+3x+2=x−3x^2+3x+2=x-3x2+3x+2=x−3 x2+2x+5=0.x^2+2x+5=0.x2+2x+5=0. Discriminant: Δ=4−20=−16<0,\Delta=4-20=-16<0,Δ=4−20=−16<0, so no real solution.

Thus Case II gives no real solution.


  1. Therefore the real solutions are x=−2,  0.x=-2,\;0.x=−2,0. So the number of real solutions is 2.2.2.

  2. Comparing with the stored correct answer:

  • Derived answer: 2
  • Stored correct answer: A = 2

They match.

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