Q42 / 83 · NTA Abhyas (JEE Main) 2020 · Mathematics · Trigonometric Equations

The number of values of the parameter α∈0,2π for which the quadratic function sin⁡αx2+2cos⁡αx+12cos⁡α+sin⁡α is the square of a linear function is

  • A
    2
  • Correct answer
    B
    4
  • C
    6
  • D
    8

Solution

For the quadratic function to be square of a linear function

D=0
⇒4cos2⁡α-4·12sin⁡αcos⁡α+sin⁡α=0⇒2cos⁡α+sin⁡αcos⁡α-sin⁡α=0
⇒tan⁡α=1 or -2
For α∈0,2π there are two solutions for each.
⇒ total four values of α.

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

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