Question Paper: Applied Mathematics - 3 : Question Paper May 2016 - Electronics Engineering (Semester 3) | Mumbai University (MU)
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## Applied Mathematics - 3 - May 2016

### Electronics Engineering (Semester 3)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks.
1(a) Evaluate $\int ^{\infty}_0e^{-2t}\left ( \dfrac{\sinh t \sin t}{t} \right )dt$(5 marks) 1(b) Obtain the Fourier Series expression for
f(x) = 9-x2 in (-3,3)
(5 marks)
1(c) Find the value of 'p' sucj that the function f(z) expressed in polar co-ordinates as
f(z) = r3 cos p&theta
(5 marks)
1(d) If $\bar{F}=(y^2-z^2+3yz-2x)\hat{i}+(3xz+2xy)\hat{j}+(3xy-2xz+2z)\hat{k}.$
Show that $\bar{F}$ is irrotational and solenoidal.
(5 marks)
2(a) Solve the differential equation using Laplace Transform $\dfrac{d^2y}{dt^2}+4\frac{dy}{dt}+8y=1$, given y(0)=0 and y'(0)=1(6 marks) 2(b) Prove that $$J_4(x)=\left ( \dfrac{48}{x^3}-\dfrac{8}{x} \right )J_1(x)-\left ( \dfrac{24}{x^2}-1 \right )J_0(x)$$(6 marks) 2(c)(i) Find the directional derivative of ϕ = 4xz3 - 3x2y2z at (2,-1,2) in the direction of $2\hat{i}+3\hat{j}+6\hat{k}.$(8 marks) 2(c)(ii) if $\bar{r}=x\hat{i}+y\hat{j}+z\hat{k}$
prove that $\nabla \log r=\dfrac{\bar{r}}{r^2}$
(8 marks)
3(a) Show that { cosx, cos2x, cos3x.....} is a set of orthogonal fundtions over (-π, π), Hence construct an orthogonal set.(6 marks) 3(b) Find an analytic function f(z)=u+iy where. $$u=\dfrac{x}{2}\log(x^2+y^2)-y\tan^{-1}\left ( \dfrac{y}{x} \right )+\sin x \cosh y$$(6 marks)

### Find the Laplace transform of

3(c)(i) $\int ^1_0 ue^{-3u}\cos^2u du$(4 marks) 3(c)(ii) $t\sqrt{1+\sin t}$(4 marks) 4(a) Find the Fourier Series for $f(x)=\dfrac{3x^2-6\pi x+2\pi^2}{12}$ in (0,2π)
Hence deduce that $\dfrac{1}{1^2}+\dfrac{1}{2^2}+\dfrac{1}{3^2}\cdots=\dfrac{\pi^2}{6}$
(6 marks)
4(b) Prove that $$\int ^b_0 xJ_0(ax)dx=\dfrac{b}{a}J_1(ab)$$(6 marks)

### Find

4(c)(i) $L^{-1}\left [ \log\left ( \dfrac{s^2+1}{s(s+1)} \right ) \right ]$(4 marks) 4(c)(ii) $L^{-1}\left [ \log\left ( \dfrac{s+2}{s^2-2s+17} \right ) \right ]$(4 marks) 5(a) Obtain the half range cosine series for \begin {align*} f(x)&=x, 0\ltx\lt\frac{\pi}{2}\ \="" \\="" &="\pi-x," \frac{\pi}{2}\ltx\lt\pi="" \end="" {align*}<="" a="">

</x&lt;\frac{\pi}{2}>
(6 marks)
5(b) Find the Bi-linear Transformation which maps the points 1,i,-1 of z plane onto i,0,-i of w-plane(6 marks) 5(c) Verify Green's Theorem for $\int _c \overline{F} .\overline{br}$ where $\bar{F}=(x^2-xy)\hat{i}+(x^2-y^2)\hat{j}$ and C is the curve bounded by x2 = 2y and x=y(8 marks) 6(a) Show that the transformation $w=\dfrac{i-iz}{1+z}$ maps the unit circle |z|=1 into real axis of w plane.(6 marks) 6(b) Using Convolution theorem find $$L^{-1}\left [ \dfrac{s}{(s^2+1)(s^2+4)} \right ]$$(6 marks) 6(c)(i) Use Gauss Divergence Theorem to evaluate $\iint _s \bar{F}.\hat{n}ds\ \text{where}\ \bar{F}=x\hat{i}+y\hat{j}+z\hat{k}$ and S is the sphere x2 + y2 + z2 = 9 and $\hat{n}$ is the outward normal to S(8 marks) 6(c)(ii) Use Stoke's Theorem to evaluate $\int _c\overline{F}.\overline{dr}\ \text{where}\ \bar{F}=x^2\hat{i}-xy\hat{j}$ and C is the square in the plane z=0 and bounded by x=0, y=0, x=a and y=a.(8 marks)