Cauchy Riemann Equations and Analytic Functions - Question Bank

1. If f(z) = u + iv is analytic, then f'(z) can be expressed using polar coordinates (r, θ) as:
A) e^(-iθ) (∂u/∂r + i ∂v/∂r)
B) e^(iθ) (∂u/∂r + i ∂v/∂r)
C) ∂u/∂r + i ∂v/∂r
D) ∂u/∂θ + i ∂v/∂θ
2. Which form of the Cauchy-Riemann equations is used when representing f in terms of z and z̄?
A) ∂f/∂z̄ = 0
B) ∂f/∂z = 0
C) ∂f/∂x = 0
D) ∂f/∂y = 0
3. If f(z) is analytic in a domain D, then f(z) is necessarily:
A) Continuous in D.
B) Differentiable in D.
C) Harmonic in D.
D) Bounded in D.
4. The function f(z) = |z| is:
A) Not analytic anywhere.
B) Analytic everywhere.
C) Differentiable only at z=0.
D) Continuous everywhere.
5. For f(z) = e^(x+iy), what are u and v?
A) u = e^x cos y, v = e^x sin y
B) u = e^x sin y, v = e^x cos y
C) u = e^x, v = e^y
D) u = cos y, v = sin y
6. If f(z) = u + iv is analytic, and f'(z) = 2z, then f(z) is:
A) z² + C
B) z²
C) 2z + C
D) z + C
7. If f(z) = x² + i y², is f(z) analytic?
A) No, it fails Cauchy-Riemann equations.
B) Yes, it is analytic everywhere.
C) No, it is only differentiable at z=0.
D) Yes, it is analytic except at z=0.
8. The converse of the Cauchy-Riemann equations (i.e., if CR equations hold, is the function analytic?) is true if:
A) The first partial derivatives of u and v are continuous.
B) The function is continuous.
C) The function is differentiable.
D) The second partial derivatives exist.
9. If f(z) = u + iv is analytic and v(x, y) = e^x sin y, what is u(x, y) up to an additive constant?
A) e^x cos y
B) -e^x cos y
C) e^y sin x
D) e^y cos x
10. If f(z) = u + iv is analytic and u(x, y) = x², what is v(x, y) up to an additive constant?
A) -2xy
B) 2xy
C) x²
D) y²
11. Which of the following is a consequence of the Cauchy-Riemann equations?
A) The real and imaginary parts are harmonic.
B) The function is always real-valued.
C) The function is always purely imaginary.
D) The function is constant.
12. If f(z) = u + iv is analytic, then f'(z) = 0 implies that f(z) is:
A) A constant function.
B) An odd function.
C) An even function.
D) A purely imaginary function.
13. The condition u_x = v_y and u_y = -v_x is known as the:
A) Cauchy-Riemann equations.
B) Laplace equation.
C) Poincare equation.
D) Euler-Lagrange equation.
14. If f(z) is analytic in a simply connected domain D, then f'(z) is also:
A) Analytic in D.
B) Continuous in D.
C) Differentiable in D.
D) Harmonic in D.
15. The function f(z) = log(z) is analytic in the complex plane except for:
A) The non-positive real axis.
B) The positive real axis.
C) The imaginary axis.
D) The origin.
16. If f(z) = e^z, then f'(z) is:
A) e^z
B) e^x
C) e^y
D) ze^(z-1)
17. If f(z) = sin(z), then f'(z) is:
A) cos(z)
B) -cos(z)
C) sin(z)
D) -sin(z)
18. If f(z) = cos(z), then f'(z) is:
A) -sin(z)
B) sin(z)
C) cos(z)
D) -cos(z)
19. The derivative of an analytic function f(z) = u + iv at a point z₀ can be computed using only the partial derivatives of u and v at z₀ as:
A) ∂u/∂x + i ∂v/∂x
B) ∂u/∂y + i ∂v/∂y
C) ∂v/∂x + i ∂u/∂x
D) ∂v/∂y + i ∂u/∂y
20. Let f(z) = u + iv be analytic. If u(x, y) = ln(x² + y²), what is v(x, y) up to an additive constant?
A) -tan⁻¹(y/x)
B) tan⁻¹(y/x)
C) ln(x² + y²)
D) -ln(x² + y²)
21. If f(z) = z * |z|², is f(z) analytic?
A) No, only differentiable at z=0.
B) Yes, analytic everywhere.
C) No, not even differentiable at z=0.
D) Yes, analytic except at z=0.
22. The Cauchy-Riemann equations provide a necessary condition for a function to be analytic. What additional condition is needed?
A) The continuity of the first partial derivatives.
B) The continuity of the function itself.
C) The harmonic nature of the real and imaginary parts.
D) The existence of the second partial derivatives.
23. If f(z) = u(x, y) + iv(x, y) is analytic, and u(x, y) = x² - y², then what is v(x, y) up to an additive constant?
A) 2xy
B) -2xy
C) x² + y²
D) y² - x²
24. Which of the following is an analytic function?
A) f(z) = z̄
B) f(z) = Re(z)
C) f(z) = Im(z)
D) f(z) = z³
25. If f(z) = u + iv is analytic, then ∂²v/∂x² + ∂²v/∂y² equals:
A) 0
B) 1
C) u
D) v
26. The function f(z) = 1/z is analytic in its domain of definition. What is its domain?
A) All complex numbers except z = 0.
B) All complex numbers.
C) The open disk |z| < 1.
D) The closed disk |z| >= 1.
27. If f(z) = z + 1/z, what is f'(z)?
A) 1 - 1/z²
B) 1 + 1/z²
C) 1 - 1/z
D) 1 + 1/z
28. The function f(z) = x + iy is:
A) Analytic everywhere.
B) Not analytic anywhere.
C) Analytic only at z = 0.
D) Differentiable everywhere but not analytic.
29. If f(z) = u + iv is analytic, then f'(z) can also be written as:
A) f'(z) = ∂v/∂y - i ∂u/∂y
B) f'(z) = ∂v/∂x - i ∂u/∂x
C) f'(z) = ∂u/∂y + i ∂v/∂y
D) f'(z) = ∂u/∂x + i ∂u/∂y
30. If u(x, y) = e^x cos y, find its harmonic conjugate v(x, y) such that f(z) = u + iv is analytic.
A) v = e^x sin y
B) v = -e^x sin y
C) v = e^y cos x
D) v = e^y sin x
31. If u(x, y) = x² - y², find its harmonic conjugate v(x, y) such that f(z) = u + iv is analytic.
A) v = 2xy
B) v = -2xy
C) v = x² + y²
D) v = y² - x²
32. The function v(x, y) is called the harmonic conjugate of u(x, y) if:
A) f(z) = u + iv is analytic.
B) u and v are harmonic.
C) u and v satisfy the Cauchy-Riemann equations.
D) f(z) is differentiable.
33. If f(z) is analytic, the function u(x, y) is said to be:
A) Harmonic.
B) Analytic.
C) Holomorphic.
D) Entire.
34. If f(z) = u(x, y) + iv(x, y) is analytic, then ∂²u/∂x² + ∂²u/∂y² equals:
A) 0
B) 1
C) u
D) v
35. The function f(z) = Im(z) = y is:
A) Not analytic anywhere.
B) Analytic everywhere.
C) Analytic only at z = 0.
D) Differentiable everywhere but not analytic.
36. The function f(z) = Re(z) = x is:
A) Not analytic anywhere.
B) Analytic everywhere.
C) Analytic only at z = 0.
D) Differentiable everywhere but not analytic.
37. Consider f(z) = e^x (cos y + i sin y). Which of the following is true?
A) f(z) is analytic and f'(z) = e^z.
B) f(z) is analytic and f'(z) = e^x (cos y + i sin y).
C) f(z) is not analytic.
D) f(z) satisfies the Cauchy-Riemann equations only at z = 0.
38. If f(z) is analytic in a domain D, then f'(z) exists at every point in D and is given by:
A) f'(z) = ∂u/∂x + i ∂v/∂x
B) f'(z) = ∂u/∂y + i ∂v/∂y
C) f'(z) = ∂u/∂x - i ∂u/∂y
D) f'(z) = ∂v/∂y - i ∂v/∂x
39. The function f(z) = |z|² is:
A) Differentiable only at z = 0.
B) Analytic everywhere.
C) Continuous everywhere but not differentiable.
D) Not continuous at z = 0.
40. For f(z) = x³ - 3xy² + i(3x²y - y³), what are ∂u/∂y and -∂v/∂x?
A) ∂u/∂y = -6xy, -∂v/∂x = -(6xy) = -6xy
B) ∂u/∂y = 6xy, -∂v/∂x = -(6xy) = -6xy
C) ∂u/∂y = -6xy, -∂v/∂x = 6xy
D) ∂u/∂y = 3y², -∂v/∂x = -3x²
41. For f(z) = x³ - 3xy² + i(3x²y - y³), what are ∂u/∂x and ∂v/∂y?
A) ∂u/∂x = 3x² - 3y², ∂v/∂y = 3x² - 3y²
B) ∂u/∂x = 3x² - 3y², ∂v/∂y = 3y² - 3x²
C) ∂u/∂x = 3x² + 3y², ∂v/∂y = 3x² + 3y²
D) ∂u/∂x = x³ - 3y², ∂v/∂y = x² - y³
42. Which of the following functions is NOT analytic at z = 0?
A) f(z) = z³
B) f(z) = e^z
C) f(z) = sin(z)
D) f(z) = 1/z
43. The condition that the partial derivatives of u and v are continuous is:
A) Necessary and sufficient for analyticity.
B) Sufficient but not necessary for analyticity.
C) Necessary but not sufficient for analyticity.
D) Neither necessary nor sufficient for analyticity.
44. If f(z) is analytic, then its real and imaginary parts, u and v, are:
A) Harmonic functions.
B) Analytic functions themselves.
C) Entire functions.
D) Meromorphic functions.
45. A function f(z) is analytic in a domain D if it is:
A) Differentiable at every point in D.
B) Continuous at every point in D.
C) Harmonic at every point in D.
D) Bounded at every point in D.
46. For f(z) = z², what are the components u(x, y) and v(x, y)?
A) u = x² - y², v = 2xy
B) u = x² + y², v = 2xy
C) u = 2xy, v = x² - y²
D) u = x², v = y²
47. If f(z) = z², what are the Cauchy-Riemann equations satisfied by u(x, y) and v(x, y)?
A) 2x = 2y and 2y = -2x
B) 2x = -2y and 2y = 2x
C) 2x = 2x and 2y = 2y
D) x = y and y = -x
48. The Cauchy-Riemann equations for a function f(z) = u(x, y) + iv(x, y) are given by:
A) u_x = v_y, u_y = -v_x
B) u_x = -v_y, u_y = v_x
C) u_x = v_x, u_y = v_y
D) u_x = -v_x, u_y = -v_y
49. If a function f(z) = u(x, y) + iv(x, y) is analytic, which pair of partial differential equations must be satisfied?
A) ∂u/∂x = ∂v/∂y and ∂u/∂y = -∂v/∂x
B) ∂u/∂x = -∂v/∂y and ∂u/∂y = ∂v/∂x
C) ∂u/∂x = ∂v/∂x and ∂u/∂y = ∂v/∂y
D) ∂u/∂x = -∂v/∂x and ∂u/∂y = -∂v/∂y
50. What is the fundamental condition for a complex function f(z) = u(x, y) + iv(x, y) to be analytic in a region?
A) The partial derivatives of u and v are continuous and satisfy the Cauchy-Riemann equations.
B) The function f(z) is continuous and differentiable at every point in the region.
C) The real part u(x, y) and imaginary part v(x, y) are harmonic functions.
D) The function f(z) can be represented by a Taylor series in the region.