Math Problem Statement

Q29: If 0 < α < π/2 is a fixed angle, P = (cos α, sin α) and Q = (cos(α − θ), sin(α − θ)), then Q is obtained from P by: Reflection in the line through origin with slope tan(θ/2). Q30: Number of terms in (1 − x + 4/x)^n, n = 28, and the sum of coefficients of terms. Q31: A man walks 3 units NE, 4 units NW, find P in Argand plane. Q32: 8 chairs numbered 1–8, find arrangement for 2 women, 3 men.

Solution

Here is the analysis and explanation for the given questions from the image:


Q29. If 0<α<π20 < \alpha < \frac{\pi}{2} is a fixed angle, and P=(cosα,sinα)P = (\cos \alpha, \sin \alpha) and Q=(cos(αθ),sin(αθ))Q = (\cos(\alpha - \theta), \sin(\alpha - \theta)), then QQ is obtained from PP by:

  • The correct answer is (D): Reflection in the line through the origin with slope tanθ2\tan \frac{\theta}{2}.
  • Explanation: Transformations involving rotations and reflections are related to trigonometric shifts. The slope of the line tanθ2\tan \frac{\theta}{2} determines the reflection transformation here.

Q30. If the number of terms in the expansion of (1x+4x)n,x0,n=28(1 - x + \frac{4}{x})^n, \, x \neq 0, \, n = 28, then the sum of the coefficients of all the terms in this expansion is:

  • Correct Answer: 729
  • Explanation:
    • Substitute x=1x = 1 in the polynomial (1x+4x)n(1 - x + \frac{4}{x})^n.
    • The expression becomes (11+4)n=4n(1 - 1 + 4)^n = 4^n.
    • The sum of coefficients = 428=7294^{28} = 729.

Q31. A man walks a distance of 3 units towards North-East (N45EN 45^\circ E), then walks a distance of 4 units towards North-West (N45WN 45^\circ W) to reach point PP. The position of PP in the Argand plane is:

  • Correct Answer: (D) (3+4i)eiπ/4(3 + 4i)e^{i\pi/4}
  • Explanation:
    • Walking 33 units in N45EN 45^\circ E is equivalent to moving 3eiπ/43e^{i\pi/4}.
    • Walking 44 units in N45WN 45^\circ W gives 4eiπ/44e^{-i\pi/4}.
    • Combine the two: 3eiπ/4+4eiπ/4=(3+4i)eiπ/43e^{i\pi/4} + 4e^{-i\pi/4} = (3 + 4i)e^{i\pi/4}.

Q32. Eight chairs are numbered 1 to 8. Two women and three men wish to occupy one chair each. First, the women choose chairs from those numbered 1 to 4, and then the men select from the remaining chairs. The number of possible arrangements is:

  • Correct Answer: (A) 6C3×4C2^6C_3 \times ^4C_2
  • Explanation:
    • The two women can choose any 22 chairs from the 44 specific ones: 4C2^4C_2.
    • The remaining 66 chairs are available, and the three men select from them: 6C3^6C_3.
    • Total combinations: 6C3×4C2^6C_3 \times ^4C_2.

Do you want further clarification or more detailed calculations for any question?


Relative Questions:

  1. How are transformations (like rotation or reflection) represented mathematically in trigonometry?
  2. What is the general formula to calculate the number of terms in a multinomial expansion?
  3. How are directions and distances converted into complex numbers in the Argand plane?
  4. What are the properties of combinations and permutations in probability?
  5. How would the answer to Q32 change if there were different restrictions on chair selection?

Tip:

For combinatorial problems, focus on breaking them into stages and use systematic counting techniques (like permutations or combinations) to simplify calculations.

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Math Problem Analysis

Mathematical Concepts

Trigonometric Transformations
Polynomial Expansion
Complex Numbers and Argand Plane
Combinatorics

Formulas

Reflection line: y = tan(θ/2)x
Sum of coefficients: Substitute x = 1 in polynomial
Argand plane: r * e^(iθ)
Combination formula: nCr = n! / [r!(n − r)!]

Theorems

Trigonometric Transformation Theorems
Binomial Expansion Theorem
Complex Number Addition
Permutation and Combination Principles

Suitable Grade Level

Grades 11-12