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Quadratic Equation and Inequalities question

2025 · 8 Apr · Shift 2 · Q33
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Quadratic Equation and Inequalities question

2025 · 8 Apr · Shift 2 · Q33

JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
The sum of the squares of the roots of ∣x−2∣2+∣x−2∣−2=0|x-2|^2 + |x-2| - 2 = 0∣x−2∣2+∣x−2∣−2=0 and the squares of the roots of x2−2∣x−3∣−5=0x^2 - 2|x-3| - 5 = 0x2−2∣x−3∣−5=0, is
  1. A
    24
  2. B
    26
  3. C
    36
  4. D
    30
View written solutionFree

Correct answer: C

  1. Solve ∣x−2∣2+∣x−2∣−2=0|x-2|^2 + |x-2| - 2 = 0∣x−2∣2+∣x−2∣−2=0

Let y=∣x−2∣y=|x-2|y=∣x−2∣ Then y≥0y\ge 0y≥0, and the equation becomes y2+y−2=0y^2+y-2=0y2+y−2=0 Factorizing, (y+2)(y−1)=0(y+2)(y-1)=0(y+2)(y−1)=0 So, y=1ory=−2y=1 \quad \text{or} \quad y=-2y=1ory=−2 Since y≥0y\ge 0y≥0, only y=1y=1y=1 is valid.

Thus, ∣x−2∣=1|x-2|=1∣x−2∣=1 So, x−2=±1x-2=\pm 1x−2=±1 Hence roots are x=3,  1x=3,\;1x=3,1 Their squares are 32=9,12=13^2=9,\quad 1^2=132=9,12=1 Sum of squares from first equation: 9+1=109+1=109+1=10


  1. Solve x2−2∣x−3∣−5=0x^2-2|x-3|-5=0x2−2∣x−3∣−5=0

We split into cases.

Case 1: x≥3x\ge 3x≥3

Then ∣x−3∣=x−3|x-3|=x-3∣x−3∣=x−3. Equation becomes x2−2(x−3)−5=0x^2-2(x-3)-5=0x2−2(x−3)−5=0 x2−2x+6−5=0x^2-2x+6-5=0x2−2x+6−5=0 x2−2x+1=0x^2-2x+1=0x2−2x+1=0 (x−1)2=0(x-1)^2=0(x−1)2=0 So x=1x=1x=1. But this does not satisfy x≥3x\ge 3x≥3, so reject.

Case 2: x<3x<3x<3

Then ∣x−3∣=3−x|x-3|=3-x∣x−3∣=3−x. Equation becomes x2−2(3−x)−5=0x^2-2(3-x)-5=0x2−2(3−x)−5=0 x2−6+2x−5=0x^2-6+2x-5=0x2−6+2x−5=0 x2+2x−11=0x^2+2x-11=0x2+2x−11=0 So, x=−2±4+442=−2±482=−2±432=−1±23x=\frac{-2\pm\sqrt{4+44}}{2}=\frac{-2\pm\sqrt{48}}{2}=\frac{-2\pm 4\sqrt{3}}{2}=-1\pm 2\sqrt{3}x=2−2±4+44​​=2−2±48​​=2−2±43​​=−1±23​ Now check x<3x<3x<3:

  • −1+23≈2.464<3-1+2\sqrt{3}\approx 2.464<3−1+23​≈2.464<3 valid
  • −1−23<3-1-2\sqrt{3}<3−1−23​<3 valid

So roots are x=−1+23,−1−23x=-1+2\sqrt{3},\quad -1-2\sqrt{3}x=−1+23​,−1−23​

Their squares sum is (−1+23)2+(−1−23)2(-1+2\sqrt{3})^2+(-1-2\sqrt{3})^2(−1+23​)2+(−1−23​)2 Use identity: (a+b)2+(a−b)2=2(a2+b2)(a+b)^2+(a-b)^2=2(a^2+b^2)(a+b)2+(a−b)2=2(a2+b2) Here a=−1a=-1a=−1, b=23b=2\sqrt{3}b=23​. So, 2[(−1)2+(23)2]=2(1+12)=262\left[(-1)^2+(2\sqrt{3})^2\right]=2(1+12)=262[(−1)2+(23​)2]=2(1+12)=26


  1. Total sum

10+26=3610+26=3610+26=36

So the correct option is C: 36\boxed{\text{C: }36}C: 36​


  1. Comparison with stored answer

Stored correct answer: C

Our derived answer is also C.

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