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Quadratic Equation and Inequalities question

2025 · 7 Apr · Shift 2 · Q32
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Quadratic Equation and Inequalities question

2025 · 7 Apr · Shift 2 · Q32

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

Correct answer: D

We need to find the number of real roots of x∣x−2∣+3∣x−3∣+1=0.x|x-2|+3|x-3|+1=0.x∣x−2∣+3∣x−3∣+1=0.

We will remove the absolute values by considering intervals based on the critical points x=2x=2x=2 and x=3x=3x=3.


1. Case-wise breakdown

The expression involves ∣x−2∣|x-2|∣x−2∣ and ∣x−3∣|x-3|∣x−3∣, so consider:

  1. x<2x<2x<2
  2. 2≤x<32\le x<32≤x<3
  3. x≥3x\ge 3x≥3

2. Case 1: x<2x<2x<2

Then ∣x−2∣=2−x,∣x−3∣=3−x.|x-2|=2-x,\qquad |x-3|=3-x.∣x−2∣=2−x,∣x−3∣=3−x. So the equation becomes x(2−x)+3(3−x)+1=0.x(2-x)+3(3-x)+1=0.x(2−x)+3(3−x)+1=0. Expand: 2x−x2+9−3x+1=02x-x^2+9-3x+1=02x−x2+9−3x+1=0 −x2−x+10=0-x^2-x+10=0−x2−x+10=0 x2+x−10=0.x^2+x-10=0.x2+x−10=0. Its roots are x=−1±1+402=−1±412.x=\frac{-1\pm\sqrt{1+40}}{2}=\frac{-1\pm\sqrt{41}}{2}.x=2−1±1+40​​=2−1±41​​. Now check which satisfy x<2x<2x<2:

  • −1+412≈2.70>2\frac{-1+\sqrt{41}}{2}\approx 2.70>22−1+41​​≈2.70>2, not valid.
  • −1−412≈−3.70<2\frac{-1-\sqrt{41}}{2}\approx -3.70<22−1−41​​≈−3.70<2, valid.

So this case gives one real root.


3. Case 2: 2≤x<32\le x<32≤x<3

Then ∣x−2∣=x−2,∣x−3∣=3−x.|x-2|=x-2,\qquad |x-3|=3-x.∣x−2∣=x−2,∣x−3∣=3−x. So the equation becomes x(x−2)+3(3−x)+1=0.x(x-2)+3(3-x)+1=0.x(x−2)+3(3−x)+1=0. Expand: x2−2x+9−3x+1=0x^2-2x+9-3x+1=0x2−2x+9−3x+1=0 x2−5x+10=0.x^2-5x+10=0.x2−5x+10=0. Discriminant: Δ=(−5)2−4(1)(10)=25−40=−15<0.\Delta = (-5)^2-4(1)(10)=25-40=-15<0.Δ=(−5)2−4(1)(10)=25−40=−15<0. Hence there are no real roots in this interval.


4. Case 3: x≥3x\ge 3x≥3

Then ∣x−2∣=x−2,∣x−3∣=x−3.|x-2|=x-2,\qquad |x-3|=x-3.∣x−2∣=x−2,∣x−3∣=x−3. So the equation becomes x(x−2)+3(x−3)+1=0.x(x-2)+3(x-3)+1=0.x(x−2)+3(x−3)+1=0. Expand: x2−2x+3x−9+1=0x^2-2x+3x-9+1=0x2−2x+3x−9+1=0 x2+x−8=0.x^2+x-8=0.x2+x−8=0. Its roots are x=−1±1+322=−1±332.x=\frac{-1\pm\sqrt{1+32}}{2}=\frac{-1\pm\sqrt{33}}{2}.x=2−1±1+32​​=2−1±33​​. Now check which satisfy x≥3x\ge 3x≥3:

  • −1+332≈2.37<3\frac{-1+\sqrt{33}}{2}\approx 2.37<32−1+33​​≈2.37<3, not valid.
  • −1−332<0\frac{-1-\sqrt{33}}{2}<02−1−33​​<0, not valid.

So this case gives no real root.


5. Total number of real roots

Adding all valid roots from the three cases:

  • Case 1: 111
  • Case 2: 000
  • Case 3: 000

Therefore, the equation has 1\boxed{1}1​ real root.


6. Option matching

Given options:

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

So the correct option is D.\boxed{\text{D}}.D​.


7. Comparison with stored answer

Stored correct answer: D

Our derived answer is also D, so they agree.

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