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Differentials and Partial Derivatives 3 Mark Book Back Question Paper With Answer Key

12th Standard

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Maths

Time : 01:00:00 Hrs
Total Marks : 144

    3 Marks

    48 x 3 = 144
  1. Find the linear approximation for f(x) = \(\sqrt { 1+x } ,x\ge -1\) at x0 = 3. Use the linear approximation to estimate f(3.2) 

  2. Use linear approximation to find an approximate value of \(\sqrt { 9.2 } \) without using a calculator.

  3. Let us assume that the shape of a soap bubble is a sphere. Use linear approximation to approximate the increase in the surface area of a soap bubble as its radius increases from 5 cm to 5.2 cm. Also, calculate the percentage error.

  4. Let \(f(x)=\sqrt [ 3 ]{ x } \). Find the linear approximation at x = 27. Use the linear approximation to approximate \(\sqrt [ 3 ]{ 27.2 } \)

  5. Find a linear approximation for the following functions at the indicated points.
    f(x) = x3 - 5x + 12, x0 = 2

  6. Find a linear approximation for the following functions at the indicated points.
    g(x) = \(g(x)=\sqrt { { x }^{ 2 }+9 } ,{ x }_{ 0 }=-4\)

  7. Find a linear approximation for the following functions at the indicated points.
    \(h(x)=\frac{x}{x+1}, x_{0}=1\)

  8. Let f, g : (a, b)→R be differentiable functions. Show that d(fg) = fdg + gdf

  9. If the radius of a sphere, with radius 10 cm, has to decrease by 0 1. cm, approximately how much will its volume decrease?

  10. Find df for f(x) = x2 + 3x and evaluate it for
    x = 2 and dx = 0.1

  11. Find df for f(x) = x2 + 3x and evaluate it for
    x = 3 and dx = 0.02

  12. Find ∆f and df for the function f for the indicated values of x, ∆x and compare
    (1) f(x) = x3 - 2x2 ; x = 2, ∆ x = dx = 0.5
    (2) f(x) = x2 + 2x + 3; x = -0.5, ∆x = dx = 0.1 

  13. Find ∆f and df for the function f for the indicated values of x, ∆x and compare

  14. Assuming log10e = 0.4343, find an approximate value of log10 1003

  15. An egg of a particular bird is very nearly spherical. If the radius to the inside of the shell is 5 mm and radius to the outside of the shell is 5.3 mm, find the volume of the shell approximately.

  16. Assume that the cross section of the artery of human is circular. A drug is given to a patient to dilate his arteries. If the radius of an artery is increased from 2 mm to 2.1 mm, how much is cross-sectional area increased approximately?

  17. Let f (x,y) = \(\frac { 3x-5y+8 }{ { x }^{ 2 }+{ y }^{ 2 }+1 } \) for all (x, y) ∈ RShow that f is continuous on R2 

  18. f(x,y) = \(\frac { xy }{ { x }^{ 2 }+{ y }^{ 2 } } \), if (x,y) ≠ (0, 0) and f (0, 0) = 0. Show that f is not continuous at (0, 0) and continuous at all other points of R2

  19. Evaluate \(\begin{gathered} \text { lim } \\ (x, y) \rightarrow(1,2) \end{gathered}\)g(x, y), if the limit exists, where g\((x,y)=\frac { { 3x }^{ 2 }-xy }{ { x }^{ 2 }+{ y }^{ 2 }+3 } \)

  20. Evaluate \(\begin{matrix} lim \\ (x,y)\rightarrow (0,0) \end{matrix}cos=\left( \frac { { x }^{ 3 }+{ y }^{ 3 } }{ x+y+2 } \right) \). If the limit exists.

  21. Show that f(x, y) = \(\frac { { x }^{ 2 }-{ y }^{ 2 } }{ { y }^{ 2 }+1 } \) is continuous at every (x, y) ∈ R2

  22. Let g(x, y) = \(\frac { { e }^{ y }sinx }{ x } \), for x ≠ 0 and g(0, 0) = 1. Show that g is continuous at (0, 0).

  23. For each of the following functions find the fx, fy, and show that fxy = fyx
    f(x, y) = \(\frac { 3x }{ y+sinx \ } \) 

  24. For each of the following functions find the fx, fy, and show that fxy = fyx
    f(x, y) = tan -1 (x/y) 

  25. For each of the following functions find the fx, fy and show that fxy = fyx
    f(x, y) = cos (x2 - 3xy)

  26. If U(x, y, z) = \(\frac { { x }^{ 2 }+{ y }^{ 2 } }{ xy } +3{ z }^{ 2 }y\), find \(\frac { \partial U }{ \partial x } ;\frac { \partial U }{ \partial y } \) and \(\frac { \partial U }{ \partial z } \)

  27. For each of the following functions find the gxy, gxx, gyy and gyx.
    g(x, y) = xey + 3x2y

  28. For each of the following functions find the gxy, gxx, gyy and gyx.
    g(x, y) = log (5x + 3y)

  29. For each of the following functions find the gxy, gxx, gyy and gyx
    g(x, y) = x2 + 3xy − 7y + cos(5x)

  30. A firm produces two types of calculators each week, x number of type A and y number of type B. The weekly revenue and cost functions (in rupees) are R(x, y) = 80x + 90y + 0.04xy − 0.05x2 − 0.05y2 and C(x, y) = 8x + 6y + 2000 respectively

  31. Let U(x, y, z) = x2 − xy + 3 sin z, x, y, z ∈ R Find the linear approximation for U at (2,−1,0).

  32. If w(x, y) = x3 − 3xy + 2y2, x, y ∊ R, find the linear approximation for w at (1,−1)

  33. Let z(x, y) = x2y + 3xy4, x, y ∈ R. Find the linear approximation for z at (2, -1).

  34. Let V(x, y, z) = xy+ yz + zx, x, y, z ∈ R. Find the differential dV.

  35. Verify the above theorem for F(x, y) = x2 - 2y2 + 2xy and x(t) = cos t, y(t) = sin t, t ∈ [0, 2\(\pi\)]

  36. Let g( x, y) = x2 - yx + sin(x+y), x(t) = e3t, y(t) = t2, t ∈ R. Find \(\frac { dg }{ dt } \) 

  37. Let g(x, y) = 2y + x2, x = 2r -s, y = r2+ 2s, r, s ∊ R. Find \(\frac { \partial g }{ \partial r } ,\frac { \partial g }{ \partial s } \)

  38. Let U(x, y, z) = xyz, x = e-t, y = e-t cos t, z = sin t, t ∈ R. Find \(\frac{dU}{dt}\)

  39. If z(x, y) = x tan-1 (xy), x = t2, y = set, s, t ∈ R. Find \(\frac { \partial z }{ \partial s } \) and \(\frac { \partial z }{ \partial t } \) at s = t = 1

  40. Let U(x, y) = ex sin y, where x = st2, y = s2 t, s, t ∈ R. Find \(\frac { \partial U }{ \partial s } ,\frac { \partial U }{ \partial t } \) and evaluate them at s = t = 1.

  41. Let z(x, y) = x3 - 3x2y3, where x = set, y = se-t, s, t ∈ R. Find \(\frac { \partial z }{ \partial s } \) and \(\frac { \partial z }{ \partial t } \)

  42. Prove that f(x, y) = x3 - 2x2y + 3xy2 + y3 is homogeneous; what is the degree? Verify Euler's Theorem for f.

  43. prove that g(x, y) = x log\(\left( \frac { y }{ x } \right) \) is homogeneous; what is the degree? Verify Euler's Theorem for g.

  44. If v(x, y) = log \(\left( \frac { { x }^{ 2 }+{ y }^{ 2 } }{ x+y } \right) \), prove that \(x\frac { \partial v }{ \partial x } +y\frac { \partial u }{ \partial y } \) = 1

  45. If w(x,y, z) = log \(\left( \frac { { 5x }^{ 3 }{ y }^{ 4 }+7{ y }^{ 2 }{ xz }^{ 4 }-{ 75y }^{ 3 }{ z }^{ 4 } }{ { x }^{ 2 }+{ y }^{ 2 } } \right) \) find \(x\frac { \partial w }{ \partial x } +y\frac { \partial w }{ \partial y } +z\frac { \partial w }{ \partial z } \)

  46. If u = sin-1 \(\left( \frac { x+y }{ \sqrt { x } +\sqrt { y } } \right) \), Show that  \(x\frac { \partial u }{ \partial x } +y\frac { \partial u }{ \partial y } =\frac { 1 }{ 2 } tanu\)

  47. State Function of Function Rule Theorem.

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