Q58 / 90 · JEE Main 2023 (31 Jan Shift 1) · Mathematics

Let y=fx represent a parabola with focus -12,0 and directrix y=-12. Then S=x∈ℝ:tan-1fx+sin-1fx+1=π2:

  • Correct answer
    A
    contains exactly two elements
  • B
    contains exactly one element
  • C
    is an infinite set
  • D
    is an empty set

Solution

Equation of parabola with focus (-12, 0) and directrix y=-12 is:

x+122=y+14

⇒y=x2+x

Put f(x)=y=x+x2 in S,

tan-1xx+1+sin-1x2+x+1=π2

⇒0≤x2+x+1≤1

⇒x2+x≤0      …1

Also,

 x2+x≥0           …2

By 1 & 2, we have

x2+x=0⇒x=0,-1

S contains 2 element.

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

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