Q17 / 87 · NTA Abhyas (JEE Main) 2020 · Mathematics · Functions

Let f:-1,1→B be a function defined as fx=cot-1⁡2x31+x2. If f is both one-one and onto, then B is the interval

  • A
    0,x3
  • B
    0,2π3
  • Correct answer
    C
    π3,2π3
  • D
    π3,π

Solution

Let, y=2x31+x2

⇒3yx2-2x+3y=0
∵x∈R⇒D≥0

⇒4-12y2≥0⇒y∈-13,13
⇒-13≤2x31+x2≤13

⇒cot-1⁡-13≥cot-1⁡2x31+x2≥cot-1⁡13
2π3≥fx≥π3

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

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