Amity University Noida B.Tech Admissions 2025
ApplyAmong Top 30 National Universities for Engineering (NIRF 2024)
Piecewise Definite integration is considered one the most difficult concept.
32 Questions around this concept.
Choose the correct option
The value of $\int_{0}^{\pi}|\cos x|^3dx$ is :
Property 5
$
\int_{\mathrm{a}}^{\mathrm{b}} \mathbf{f}(\mathrm{x}) \mathrm{d} \mathbf{x}=\int_{\mathrm{a}}^{\mathrm{c}} \mathbf{f}(\mathrm{x}) \mathrm{d} \mathbf{x}+\int_{\mathbf{c}}^{\mathrm{b}} \mathbf{f}(\mathbf{x}) \mathrm{dx} \text { where } c \in \mathbb{R}
$
This property is useful when the function is in the form of piecewise or discontinuous or non-differentiable at $x=c$ in $(a, b)$.
Let
$
\begin{aligned}
& \frac{d}{d x}(F(x))=f(x) \\
& \begin{aligned}
& \int_a^c f(x) d x+\int_c^b f(x) d x \\
& \quad=\left.F(x)\right|_a ^c+\left.F(x)\right|_c ^b \\
&=F(c)-F(a)+F(b)-F(c) \\
& \quad=F(b)-F(a) \\
& \quad=\int_a^b f(x) d x
\end{aligned}
\end{aligned}
$
$
\therefore \quad \int_a^c f(x) d x+\int_c^b f(x) d x
$
The above property can also be generalized into the following form
$
\int_a^b f(x) d x=\int_a^{c_1} f(x) d x+\int_{c_1}^{c_2} f(x) d x+\ldots+\int_{c_n}^b f(x) d x
$
where, $\quad a<c_1<c_2<\ldots<c_{n-1}<c_n<b$.
Property 6
$
\int_0^a f(x) d x=\int_0^{a / 2} f(x) d x+\int_0^{a / 2} f(a-x) d x
$
Proof:
From the previous property,
$
\int_0^a f(x) d x=\int_0^{a / 2} f(x) d x+\int_{a / 2}^a f(x) d x
$
Put $x=a-t \Rightarrow d x=-d t$ in the second integral, when $x=a / 2$, then $t=a / 2$ and when $x=a$, then $t=0$
$
\therefore \quad \begin{aligned}
\int_0^a f(x) d x & =\int_0^{a / 2} f(x) d x+\int_{a / 2}^0 f(a-t)(-d t) \\
& =\int_0^{\mathrm{a} / 2} \mathrm{f}(\mathrm{x}) \mathrm{dx}+\int_0^{\mathrm{a} / 2} \mathrm{f}(\mathrm{a}-\mathrm{t}) \mathrm{dt} \\
\int_0^a f(x) d x & =\int_0^{a / 2} f(x) d x+\int_0^{a / 2} f(a-x) d x
\end{aligned}
$
"Stay in the loop. Receive exam news, study resources, and expert advice!"