Q45 / 90 · JEE Main 2022 (25 Jun Shift 1) · Mathematics

If y=m1x+c1 and y=m2x+c2, m1≠m2 are two common tangents of circle x2+y2=2 and parabola y2=x, then the value of 8 m1 m2 is equal to

  • Correct answer
    A
    32-4
  • B
    62-4
  • C
    -5+62
  • D
    3+42

Solution

Figure

Equation of the tangent to the parabola can be written as y=mx+14m or y-mx-14m=0

Now, the perpendicular distance from 0,0 to the tangent is equal to the radius of the given circle, soOM=2⇒-14m1+m2=2

⇒216m21+m2=1  ⇒32m4+32m2-1=0

⇒  m2=-25+2316+22×25 ignoring the negative sign as it is square function.

Now 8m1m2=8m2

=-25+2316+223=32-4

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

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