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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Definite Integration

NDA 2025 · Mathematics · Definite Integration

Consider the following for the two (02) items that follow: Let f(x)...

Consider the following for the two (02) items that follow:
Let f(x)=[x2]f(x) = [x^2], where [⋅][\cdot] is the greatest integer function.

What is ∫22f(x) dx\int_{\sqrt{2}}^{2} f(x) \, dx equal to?

Options

  1. A6−3−226 - \sqrt{3} - 2\sqrt{2}
  2. B6−3−26 - \sqrt{3} - \sqrt{2}
  3. C6−3+226 - \sqrt{3} + 2\sqrt{2}
  4. D6+3−226 + \sqrt{3} - 2\sqrt{2}

Correct answer

A. 6−3−226 - \sqrt{3} - 2\sqrt{2}

Step-by-step solution

The given integral is ∫22[x2] dx\int_{\sqrt{2}}^{2} [x^2] \, dx.

As xx varies from 2to2\sqrt{2} to 2, x2x^2 varies from 2to42 to 4. The greatest integer function [x2][x^2] changes its value when x2x^2 is an integer. The integer values of x2x^2 in this interval are 2,3,and42, 3, and 4, which correspond to x=2,3,and2x = \sqrt{2}, \sqrt{3}, and 2.

We split the integral at x=3x = \sqrt{3}:

For x∈(2,3)x \in (\sqrt{2}, \sqrt{3}), 2<x2<3⇒[x2]=22 < x^2 < 3 \Rightarrow [x^2] = 2

For x∈(3,2)x \in (\sqrt{3}, 2), 3<x2<4⇒[x2]=33 < x^2 < 4 \Rightarrow [x^2] = 3

The integral can be written as:

\int22[int_{\sqrt{2}}^{2} [x^2] \, dx = \int23int_{\sqrt{2}}^{\sqrt{3}}2 \, dx + \int32int_{\sqrt{3}}^{2}3 \, dx

Evaluating the integrals:<br><br>∫232 dx=2[x]23=2(3−2)=23−22integrals:<br><br>\int_{\sqrt{2}}^{\sqrt{3}} 2 \, dx = 2[x]_{\sqrt{2}}^{\sqrt{3}} = 2(\sqrt{3} - \sqrt{2}) = 2\sqrt{3} - 2\sqrt{2}

∫323 dx=3[x]32=3(2−3)=6−33\int_{\sqrt{3}}^{2} 3 \, dx = 3[x]_{\sqrt{3}}^{2} = 3(2 - \sqrt{3}) = 6 - 3\sqrt{3}

Adding the two values:

∫22[x2] dx=(23−22)+(6−33)\int_{\sqrt{2}}^{2} [x^2] \, dx = (2\sqrt{3} - 2\sqrt{2}) + (6 - 3\sqrt{3})

∫22[x2] dx=6−3−22\int_{\sqrt{2}}^{2} [x^2] \, dx = 6 - \sqrt{3} - 2\sqrt{2}

Answer: $6 - \sqrt{3} - 2\sqrt{2}
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