MCQMediumJEE 2024Simple Applications

JEE Mathematics 2024 Question with Solution

Let aa be the sum of all coefficients in the expansion of (12x+2x2)2023(34x2+2x3)2024\left(1-2x+2x^2\right)^{2023}\left(3-4x^2+2x^3\right)^{2024}. If the equations cx2+dx+e=0cx^2+dx+e=0 and 2bx2+ax+4=02bx^2+ax+4=0 have a common root, then c:d:ec:d:e equals:

  • A

    2:1:42:1:4

  • B

    4:1:44:1:4

  • C

    1:2:41:2:4

  • D

    1:1:41:1:4

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: aa is the sum of all coefficients of (12x+2x2)2023(34x2+2x3)2024\left(1-2x+2x^2\right)^{2023}\left(3-4x^2+2x^3\right)^{2024}. The equations cx2+dx+e=0cx^2+dx+e=0 and 2bx2+ax+4=02bx^2+ax+4=0 have a common root.

Find: The ratio c:d:ec:d:e.

From the solution, the sum of coefficients is obtained by substituting x=1x=1:

(121+212)2023(3412+213)2024=1202312024=1\left(1-2\cdot1+2\cdot1^2\right)^{2023}\left(3-4\cdot1^2+2\cdot1^3\right)^{2024}=1^{2023}\cdot1^{2024}=1

Hence, a=1a=1.

The solution then concludes that the correct option is D and states the required ratio as 1:1:41:1:4.

There is inconsistency in the extracted working for bb and in the intermediate justification, but the solution explicitly identifies D as the correct option.

Therefore, the correct option is D, so c:d:e=1:1:4c:d:e=1:1:4.

Common mistakes

  • Using the sum of coefficients incorrectly. For a polynomial, the sum of coefficients is found by substituting x=1x=1, not by adding visible terms manually. Evaluate the entire expression at x=1x=1 first.

  • Assuming every line of the extracted solution is internally consistent. Here the intermediate working for bb is contradictory, so the final marked option on the solution must be treated.

  • Mixing up the ratio order. The question asks for c:d:ec:d:e, so even if intermediate symbols are discussed in a different order, the final comparison must be made in the exact order requested.

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