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Straight Lines and Pair of Straight Lines question

2024 · 6 Apr · Shift 2 · Q49
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Straight Lines and Pair of Straight Lines question

2024 · 6 Apr · Shift 2 · Q49

JEE MainMathematicsStraight Lines and Pair of Straight LinesMCQ+4 / −1
If the locus of the point, whose distances from the point (2,1)(2,1)(2,1) and (1,3)(1,3)(1,3) are in the ratio 5:45: 45:4, is ax2+by2+cxy+dx+ey+170=0a x^2+b y^2+c x y+d x+e y+170=0ax2+by2+cxy+dx+ey+170=0, then the value of a2+2b+3c+4d+ea^2+2 b+3 c+4 d+ea2+2b+3c+4d+e is equal to :
  1. A
    37
  2. B
    −27-27−27
  3. C
    437
  4. D
    5
View written solutionFree

Correct answer: A

  1. Let the moving point be P(x,y)P(x,y)P(x,y).

    Its distances from (2,1)(2,1)(2,1) and (1,3)(1,3)(1,3) are in the ratio 5:45:45:4. So, (x−2)2+(y−1)2(x−1)2+(y−3)2=54\frac{\sqrt{(x-2)^2+(y-1)^2}}{\sqrt{(x-1)^2+(y-3)^2}}=\frac{5}{4}(x−1)2+(y−3)2​(x−2)2+(y−1)2​​=45​

  2. Squaring both sides: (x−2)2+(y−1)2(x−1)2+(y−3)2=2516\frac{(x-2)^2+(y-1)^2}{(x-1)^2+(y-3)^2}=\frac{25}{16}(x−1)2+(y−3)2(x−2)2+(y−1)2​=1625​

    Hence, 16[(x−2)2+(y−1)2]=25[(x−1)2+(y−3)2]16\big[(x-2)^2+(y-1)^2\big]=25\big[(x-1)^2+(y-3)^2\big]16[(x−2)2+(y−1)2]=25[(x−1)2+(y−3)2]

  3. Expand both sides.

    Left side: 16[(x2−4x+4)+(y2−2y+1)]16\left[(x^2-4x+4)+(y^2-2y+1)\right]16[(x2−4x+4)+(y2−2y+1)] =16(x2+y2−4x−2y+5)=16(x^2+y^2-4x-2y+5)=16(x2+y2−4x−2y+5) =16x2+16y2−64x−32y+80=16x^2+16y^2-64x-32y+80=16x2+16y2−64x−32y+80

    Right side: 25[(x2−2x+1)+(y2−6y+9)]25\left[(x^2-2x+1)+(y^2-6y+9)\right]25[(x2−2x+1)+(y2−6y+9)] =25(x2+y2−2x−6y+10)=25(x^2+y^2-2x-6y+10)=25(x2+y2−2x−6y+10) =25x2+25y2−50x−150y+250=25x^2+25y^2-50x-150y+250=25x2+25y2−50x−150y+250

  4. Bring all terms to one side: 16x2+16y2−64x−32y+80−25x2−25y2+50x+150y−250=016x^2+16y^2-64x-32y+80-25x^2-25y^2+50x+150y-250=016x2+16y2−64x−32y+80−25x2−25y2+50x+150y−250=0

    −9x2−9y2−14x+118y−170=0-9x^2-9y^2-14x+118y-170=0−9x2−9y2−14x+118y−170=0

    Multiplying by −1-1−1: 9x2+9y2+14x−118y+170=09x^2+9y^2+14x-118y+170=09x2+9y2+14x−118y+170=0

  5. Compare with ax2+by2+cxy+dx+ey+170=0ax^2+by^2+cxy+dx+ey+170=0ax2+by2+cxy+dx+ey+170=0

    So, a=9,b=9,c=0,d=14,e=−118a=9,\quad b=9,\quad c=0,\quad d=14,\quad e=-118a=9,b=9,c=0,d=14,e=−118

  6. Compute the required value: a2+2b+3c+4d+ea^2+2b+3c+4d+ea2+2b+3c+4d+e =92+2(9)+3(0)+4(14)−118=9^2+2(9)+3(0)+4(14)-118=92+2(9)+3(0)+4(14)−118 =81+18+0+56−118=81+18+0+56-118=81+18+0+56−118 =37=37=37

  7. Therefore, the correct option is: 37\boxed{37}37​ i.e. Option A.

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