Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Definite Integration

Question:

$\int\limits_{-2}^2 \min (x-[x],-x-[-x]) d x$, where [.] is the greatest integer function =

Options:

0

1

2

None of these

Correct Answer:

1

Explanation:

Let $I=\int\limits_{-2}^2 \min (x-[x],-x-[-x]) d x$

$=2 \int\limits_0^2 \min (x-[x],-x-[-x]) d x$         (∵ function is even)

$\min (x-[x],-x-[-x])=\left\{\begin{array}{l}x, 0 \leq x<\frac{1}{2} \\ -x+1, \frac{1}{2} \leq x<1 \\ x-1,1 \leq x<\frac{3}{2} \\ -x+2, \frac{3}{2} \leq x<2\end{array}\right.$

∴  $I=2 \int\limits_0^{\frac{1}{2}} x d x+2 \int\limits_{\frac{1}{2}}^1(-x+1) d x+2 \int\limits_1^{\frac{3}{2}}(x-1) d x+ 2 \int\limits_{\frac{3}{2}}^2(-x+2) d x$

$=2\left[\frac{x^2}{2}\right]_0^{\frac{1}{2}}+2\left[-\frac{x^2}{2}+x\right]_{\frac{1}{2}}^1+2\left[\frac{x^2}{2}-x\right]_1^{\frac{3}{2}}+2\left[-\frac{x^2}{2}+2 x\right]_{\frac{3}{2}}^2$

$=\frac{1}{4}+\frac{1}{4}+\frac{1}{4}+\frac{1}{4}=1$

Hence $I = 1$