NVAMediumJEE 2023Indefinite Integrals

JEE Mathematics 2023 Question with Solution

Let for xR,S0(x)=x,Sk(x)=Ckx+k0xSk1(t)dtx \in \mathbb{R}, \, S_0(x) = x, \, S_k(x) = C_k x + k \int_0^x S_{k-1}(t) \, dt where C0=1,Ck=101Sk1(x)dx,k=1,2,3,C_0 = 1, \, C_k = 1 - \int_0^1 S_{k-1}(x) \, dx, \, k = 1, 2, 3, \dots. Then S2(3)+6C3S_2(3) + 6C_3 is equal to:

Answer

Correct answer:18

Step-by-step solution

the solution unavailable

Working could not be extracted because the solution is unavailable. Using the provided correct answer field, the numerical value is 1818.

Common mistakes

  • Using the recursion for Sk(x)S_k(x) without first computing CkC_k. This is wrong because each Sk(x)S_k(x) depends explicitly on the corresponding constant CkC_k. Always evaluate Ck=101Sk1(x)dxC_k = 1 - \int_0^1 S_{k-1}(x) \, dx before forming Sk(x)S_k(x).

  • Confusing the variable of integration inside 0xSk1(t)dt\int_0^x S_{k-1}(t) \, dt with the outer variable xx. This can lead to incorrect antiderivatives. Treat tt as the dummy variable and substitute the upper limit only after integration.

  • Substituting directly into C3C_3 without computing S2(x)S_2(x) on the full interval [0,1][0,1]. This is wrong because C3C_3 depends on 01S2(x)dx\int_0^1 S_2(x) \, dx, not merely on the value S2(3)S_2(3). Compute the entire function first, then integrate.

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