Semester A

כימיה כללית ופיזיקלית

Semester B

פיזיקה

כימיה אורגנית

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Common Patterns and Tips:

Question 1: Evaluate Inverse Functions

Visualization of basic inverse trigonometric functions

Find the values of:

  1. \(\sin^{-1}(-\sqrt{3}/2)\)
  2. \(\tan^{-1}(1) - \tan^{-1}(-1)\)
  3. \(\cot^{-1}(1/\sqrt{3}) - \cot^{-1}(-1/\sqrt{3})\)
  4. \(\cosh^{-1}\sqrt{2}\)
  5. \(e^{[-\coth^{-1}(25/7)]}\)
  1. For \(\sin^{-1}(-\sqrt{3}/2)\):
    • This is the angle whose sine is \(-\sqrt{3}/2\)
    • We know that \(\sin(5\pi/6) = -\sqrt{3}/2\)
    • Therefore, \(\sin^{-1}(-\sqrt{3}/2) = -\pi/3\)
  2. For \(\tan^{-1}(1) - \tan^{-1}(-1)\):
    • \(\tan^{-1}(1) = \pi/4\)
    • \(\tan^{-1}(-1) = -\pi/4\)
    • Therefore, \(\tan^{-1}(1) - \tan^{-1}(-1) = \pi/2\)
  3. For \(\cot^{-1}(1/\sqrt{3}) - \cot^{-1}(-1/\sqrt{3})\):
    • \(\cot^{-1}(1/\sqrt{3}) = \pi/6\)
    • \(\cot^{-1}(-1/\sqrt{3}) = 5\pi/6\)
    • Therefore, the difference is \(-\pi/3\)
  4. For \(\cosh^{-1}\sqrt{2}\):
    • By definition, \(\cosh^{-1}x = \ln(x + \sqrt{x^2-1})\)
    • Substituting \(x = \sqrt{2}\)
    • Result is \(\ln(1 + \sqrt{2})\)
  5. For \(e^{[-\coth^{-1}(25/7)]}\):
    • Recall that \(\coth^{-1}x = \frac{1}{2}\ln(\frac{x+1}{x-1})\)
    • Substituting x = 25/7: \[\coth^{-1}(\frac{25}{7}) = \frac{1}{2}\ln(\frac{32/7}{18/7}) = \frac{1}{2}\ln(\frac{32}{18})\]
    • Therefore: \[e^{[-\coth^{-1}(25/7)]} = e^{-\frac{1}{2}\ln(\frac{32}{18})} = (\frac{32}{18})^{-1/2} = \frac{3}{4}\]

Answers:

  • a) \(-\pi/3\)
  • b) \(\pi/2\)
  • c) \(-\pi/3\)
  • d) \(\ln(1 + \sqrt{2})\)
  • e) \(\frac{3}{4}\)

Question 2: Special Identity

Prove that: \[\tan^{-1}x + \cot^{-1}x = \frac{\pi}{2}\] for all x

Visualization of the identity showing constant sum π/2

  1. Let's start by noting that \(\cot^{-1}x = \tan^{-1}(\frac{1}{x})\)
  2. Therefore, we need to prove: \[\tan^{-1}x + \tan^{-1}(\frac{1}{x}) = \frac{\pi}{2}\]
  3. Using the tangent addition formula: \[\tan(A + B) = \frac{\tan A + \tan B}{1 - \tan A \tan B}\]
  4. Let \(A = \tan^{-1}x\) and \(B = \tan^{-1}(\frac{1}{x})\)
  5. Then \(\tan(A + B) = \frac{x + \frac{1}{x}}{1 - x \cdot \frac{1}{x}} = \infty\)
  6. Therefore, \(A + B = \frac{\pi}{2}\)

The graph above visually confirms that this sum remains constant at π/2 for all valid x.

Question 3: Hyperbolic Function Identities

Derive the following identities:

Visualization of hyperbolic functions and their relationships

  1. Recall the definitions: \[\sinh x = \frac{e^x - e^{-x}}{2}\] \[\cosh x = \frac{e^x + e^{-x}}{2}\]
  2. For the first identity: \[\sinh(x \pm y) = \frac{e^{x\pm y} - e^{-(x\pm y)}}{2}\] \[= \frac{e^x e^{\pm y} - e^{-x} e^{\mp y}}{2}\]
  3. Expand this using the definitions above to get: \[\sinh x \cosh y \pm \cosh x \sinh y\]
  4. Similarly for the second identity, starting with: \[\cosh(x \pm y) = \frac{e^{x\pm y} + e^{-(x\pm y)}}{2}\]
  5. This expands to: \[\cosh x \cosh y \pm \sinh x \sinh y\]

The plot above shows how these functions behave and their relationships to each other.

Question 4: Triple Angle and Hyperbolic Formulas

Visualization of cos(3x) and its components

  1. For the triple angle formula: \[\cos(3x) = 4\cos^3(x) - 3\cos(x)\]
  2. Start with the double angle formula: \[\cos(2x) = 2\cos^2(x) - 1\]
  3. Then use the angle addition formula: \[\cos(3x) = \cos(2x + x)\]
  4. Substitute the double angle formula into this to get the triple angle formula
  5. For the hyperbolic formula: \[\cosh(2x) = 2\cosh^2(x) - 1\]
  6. Use the same process to derive the hyperbolic triple angle formula

Question 5: Inverse Hyperbolic Function Proofs

Visualization of inverse hyperbolic functions and their domains

  1. For the inverse hyperbolic functions: \[\text{arsinh}(x) = \ln(x + \sqrt{x^2 + 1})\] \[\text{arcosh}(x) = \ln(x + \sqrt{x^2 - 1})\] \[\text{artanh}(x) = \frac{1}{2}\ln(\frac{1+x}{1-x})\]
  2. These are derived by inverting the hyperbolic functions
  3. For the first identity: \[\text{arsinh}(x) = \ln(x + \sqrt{x^2 + 1})\]
  4. Start with \(y = \text{arsinh}(x)\) and use the definition of sinh
  5. Then solve for x to get the inverse function

Question 6: Domain Analysis

Visualization of functions with restricted domains

  1. For the domain-restricted functions: \[\ln(\sin x), \frac{1}{\sqrt{|\cos x|}}, \ln|\ln x|\]
  2. These functions have specific domains where they are defined
  3. For the first function: \[\ln(\sin x)\]
  4. Since the natural logarithm is only defined for positive values, the domain is: \[0 < \sin x \leq 1\]
  5. Similarly, analyze the other two functions to find their domains