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Differentiation
NDA 2020
Exam
NDA
Year
2020
Subject
Mathematics
Chapter
Differentiation
NDA 2020 · Mathematics · Differentiation
If e^ θ =c+4 θ , where c is an arbitrary constant and is a function...
If
e
θ
φ
=
c
+
4
θ
φ
e^{\theta \varphi}=c+4 \theta \varphi
e
θφ
=
c
+
4
θφ
, where
c
c
c
is an arbitrary constant and
φ
\varphi
φ
is a function of
θ
\theta
θ
, then what is
φ
d
θ
\varphi \mathrm{d} \theta
φ
d
θ
equal to?
Options
A
θ
d
φ
\theta \mathrm{d} \varphi
θ
d
φ
B
−
θ
d
φ
-\theta \mathrm{d} \varphi
−
θ
d
φ
C
4
θ
d
φ
4 \theta \mathrm{ d} \varphi
4
θ
d
φ
D
−
4
θ
d
φ
-4 \theta \mathrm{ d} \varphi
−
4
θ
d
φ
Correct answer
B.
−
θ
d
φ
-\theta \mathrm{d} \varphi
−
θ
d
φ
Step-by-step solution
e
θ
ϕ
=
C
+
4
θ
⋅
ϕ
(
θ
⋅
ϕ
)
ln
e
=
ln
(
C
+
4
θ
⋅
ϕ
)
θ
⋅
ϕ
=
ln
(
C
+
4
θ
⋅
ϕ
)
⇒
θ
⋅
g
ϕ
=
4
{
ln
(
θ
)
+
ln
(
ϕ
)
}
+
ln
C
\begin{aligned} & e^{\theta \phi}=C+4 \theta \cdot \phi \\ & \text{ ( } \theta \cdot \phi) \ln e=\ln (C+4 \theta \cdot \phi) \\ & \theta \cdot \phi=\ln (C+4 \theta \cdot \phi) \\ & \Rightarrow \theta \cdot g \phi=4\{\ln (\theta)+\ln (\phi)\}+\ln C \end{aligned}
e
θϕ
=
C
+
4
θ
⋅
ϕ
(
θ
⋅
ϕ
)
ln
e
=
ln
(
C
+
4
θ
⋅
ϕ
)
θ
⋅
ϕ
=
ln
(
C
+
4
θ
⋅
ϕ
)
⇒
θ
⋅
g
ϕ
=
4
{
ln
(
θ
)
+
ln
(
ϕ
)}
+
ln
C
Differentiating both sides with respect to '
θ
\theta
θ
'.
ϕ
+
θ
⋅
d
ϕ
d
θ
=
4
(
1
θ
+
1
ϕ
⋅
d
ϕ
d
θ
)
ϕ
⋅
d
θ
+
θ
⋅
d
ϕ
=
4
ϕ
⋅
d
θ
+
4
⋅
θ
⋅
d
ϕ
\begin{aligned} & \phi+\theta \cdot \frac{d \phi}{d \theta}=4\left(\frac{1}{\theta}+\frac{1}{\phi} \cdot \frac{d \phi}{d \theta}\right) \\ & \phi \cdot d \theta+\theta \cdot d \phi=4 \phi \cdot d \theta+4 \cdot \theta \cdot d \phi\end{aligned}
ϕ
+
θ
⋅
d
θ
d
ϕ
=
4
(
θ
1
+
ϕ
1
⋅
d
θ
d
ϕ
)
ϕ
⋅
d
θ
+
θ
⋅
d
ϕ
=
4
ϕ
⋅
d
θ
+
4
⋅
θ
⋅
d
ϕ
⇒
3
θ
⋅
d
ϕ
=
−
3
ϕ
⋅
d
θ
∴
ϕ
⋅
d
θ
=
−
θ
⋅
d
ϕ
\begin{aligned} & \Rightarrow 3 \theta \cdot d \phi=-3 \phi \cdot d \theta \\ & \therefore \phi \cdot d \theta=-\theta \cdot d \phi\end{aligned}
⇒
3
θ
⋅
d
ϕ
=
−
3
ϕ
⋅
d
θ
∴
ϕ
⋅
d
θ
=
−
θ
⋅
d
ϕ
$
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