Q40 / 90 · JEE Main 2022 (27 Jun Shift 2) · Mathematics

If the equation of the parabola, whose vertex is at 5,4 and the directrix is 3x+y-29=0, is x2+ay2+bxy+cx+dy+k=0, then a+b+c+d+k is equal to

  • A
    575
  • B
    -575
  • C
    576
  • Correct answer
    D
    -576

Solution

Given the equation of the parabola whose vertex is 5,4 and equation of directrix is 3x+y-29=0 is x2+ay2+bxy+cx+dy+e=0

Let focus be α,β

Let equation of  ZV which is perpendicular to 3x+y-29=0 be x-3y+k=0 and it passes through point 5,4.  So, k=7 and equation of ZV become x-3y+7=0

Now the intersection of 3x+y-29=0 & x-3y+7=0 will be Z=8,5

Now plotting the diagram we get,

Figure

So, foot of perpendicular from 5,4 on 3x+y-29=0 is 8,5

Now using the midpoint formula we will find the focus of parabola⇒α+82=5,β+52=4⇒α,β=2,3

∴ Focus is 2,3 and directrix is 3x+y-29=0

Applying PS2=PM2, we get

x-22+y-32=3x+y-29210

⇒x2+9y2-6xy+134x-2y-711=0

Comparing withx2+ay2+bxy+cx+dy+e=0 , we get a+b+c+d+e=9-6+134-2-711=-576

Hence, the correct answer is option: 'D'.

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