Q90 / 160 · TS EAMCET 2021 (04 Aug Shift 1) · Mathematics

If 9x2-24xy+16y2+αx+βy+6=0 represents a pair of parallel lines of 1 unit apart and one of those lines passes through (1, 1) then αβ=

  • A
    23
  • B
    1
  • C
    -32
  • Correct answer
    D
    -34

Solution

If ax2+2hxy+by2+2gx+2fy+c=0 represents a pair of parallel lines then condition applies

h2=ab & bg2=af2

Compare the given pair of lines with  ax2+2hxy+by2+2gx+2fy+c=0 ,we get

a=9,2h=-24,b=16,α=2g,β=2f,c=6

Put all given values in  bg2=af2 we get

16α24=9β24αβ2=916

αβ=±34.

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

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