Q19 / 54 · JEE Advanced 2020 (Paper 1) · Mathematics

Suppose a, b denote the distinct real roots of the quadratic polynomial x 2 +20x−2020 and suppose c, d denote the distinct complex roots of the quadratic polynomial x2-20x+2020. Then the value of aca−c+ada−d+bcb−c+bdb−d

  • A
    0
  • B
    8000
  • C
    8080
  • Correct answer
    D
    16000

Solution

Finding the sum and product of roots of the two given quadratic equations i.e.

a+b=-20 & ab=-2020 ...........i

c+d=20 & cd=2020 ...........ii

Now,  aca−c+ada−d+bcb−c+bdb−d

=a2c+d−ac2+d2+b2c+d−bc2+d2

=a2+b2c+d−a+bc2+d2

=a+b2−2abc+d−a+bc+d2−2cd

=-202−2-202020−-20202−22020 (using equations i & ii)

=16000

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

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