Mathematics · Functions

JEE Main 2025 — 3 April, Morning Shift — Question 36

Let the domain of the function f(x)=log⁡2log⁡4log⁡6(3+4x−x2)f(x)=\log _{2} \log _{4} \log _{6}\left(3+4 x-x^{2}\right) be (a,b)(a, b). If

∫0b−a[x2]dx=p−q−r,p,q,r∈N,gcd⁡(p,q,r)=1\int_{0}^{b-a}\left[x^{2}\right] d x=p-\sqrt{q}-\sqrt{r}, p, q, r \in \mathbb{N}, \operatorname{gcd}(p, q, r)=1, where [⋅][\cdot] is the greatest integer

function, then p+q+r\mathrm{p}+\mathrm{q}+\mathrm{r} is equal to

  1. Option A:

    10

    Correct
  2. Option B:

    8

  3. Option C:

    11

  4. Option D:

    9

Answer: A

Step-by-step solution

log⁡4log⁡6(3+4x−x2)>0\log _{4} \log _{6}\left(3+4 \mathrm{x}-\mathrm{x}^{2}\right)>0

log⁡6(3+4x−x2)>1\log _{6}\left(3+4 \mathrm{x}-\mathrm{x}^{2}\right)>1

3+4x−x2>63+4 x-x^{2}>6

x2−4x+3<0\mathrm{x}^{2}-4 \mathrm{x}+3<0

(x−1)(x−3)<0(x-1)(x-3)<0 x∈(1,3)x \in(1,3)

so a=1& b=3\mathrm{a}=1 \& \mathrm{~b}=3

⇒∫02[x2]dx=\Rightarrow \int_{0}^{2}\left[\mathrm{x}^{2}\right] \mathrm{dx}= ?

I=∫01[x2]dx+∫12[x2]dx+∫23[x2]dx+∫34[x2]dxI=\int_{0}^{1}\left[x^{2}\right] d x+\int_{1}^{\sqrt{2}}\left[x^{2}\right] d x+\int_{\sqrt{2}}^{\sqrt{3}}\left[x^{2}\right] d x+\int_{\sqrt{3}}^{\sqrt{4}}\left[x^{2}\right] d x

=0+∣x∣12+2∣x∣23+3∣x∣34=0+|x|_{1}^{\sqrt{2}}+2|x|_{\sqrt{2}}^{\sqrt{3}}+3|x|_{\sqrt{3}}^{\sqrt{4}}

=(2−1)+2(3−2)+3(2−3)=(\sqrt{2}-1)+2(\sqrt{3}-\sqrt{2})+3(2-\sqrt{3})

=5−2−3⇒p+q+r=10=5-\sqrt{2}-\sqrt{3} \Rightarrow \mathrm{p}+\mathrm{q}+\mathrm{r}=10

Answer key and solution verified before publishing.

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Exam
JEE Main 2025
Subject
Mathematics
Chapter
Functions
Topic
Domain & range of functions