NAPT - Navy Advanced Programs Advanced Mathematical Concepts Questions and Answers — Questions and Answers
Question 1: A submarine is on the surface, located 2,500 meters from a straight coastline. It dives at a constant angle of depression of 15 degrees. What is the submarine's depth below the surface, to the nearest meter, when it has traveled 1,000 meters horizontally towards the coastline?
- 250 meters
- 268 meters (Correct answer)
- 966 meters
- 3,732 meters
Correct answer: 268 meters
This problem can be solved using the tangent trigonometric function (SOHCAHTOA). The angle of depression from the horizontal is equal to the angle of elevation from the submarine's perspective. Let 'd' be the depth. We have tan(15°) = opposite/adjacent = d / 1000. Solving for d gives d = 1000 * tan(15°). Since tan(15°) is approximately 0.2679, the depth is 1000 * 0.2679 ≈ 268 meters.
Question 2: What is the derivative of the function f(x) = 4x³ - 7x² + 2x - 9 with respect to x?
- 12x² - 14x + 2 (Correct answer)
- 4x² - 7x + 2
- 12x³ - 14x² + 2x
- x⁴ - (7/3)x³ + x² - 9x
Correct answer: 12x² - 14x + 2
To find the derivative of a polynomial function, we use the power rule for each term, which states that the derivative of xⁿ is nxⁿ⁻¹. Applying this to each term: the derivative of 4x³ is 3 * 4x⁽³⁻¹⁾ = 12x². The derivative of -7x² is 2 * -7x⁽²⁻¹⁾ = -14x. The derivative of 2x is 1 * 2x⁽¹⁻¹⁾ = 2. The derivative of a constant (-9) is 0. Combining these results gives 12x² - 14x + 2.
Question 3: Which of the following is the correct solution for x in the logarithmic equation: log₂(x) + log₂(x - 4) = 5?
- x = -4
- x = 4
- x = 8 (Correct answer)
- x = 6
Correct answer: x = 8
First, use the logarithm product rule: log₂(x) + log₂(x - 4) = log₂(x(x - 4)). The equation becomes log₂(x² - 4x) = 5. Convert this logarithmic equation to its exponential form: 2⁵ = x² - 4x. This simplifies to 32 = x² - 4x, or x² - 4x - 32 = 0. Factoring the quadratic gives (x - 8)(x + 4) = 0. The possible solutions are x = 8 and x = -4. However, the domain of a logarithm must be positive, and log₂(-4) is undefined. Therefore, the only valid solution is x = 8.
Question 4: A complex number operation is defined as (3 + 5i) * (2 - 4i). What is the resulting complex number in the form a + bi?
- 6 - 20i
- 26 - 2i (Correct answer)
- 6 - 2i
- 26 + 2i
Correct answer: 26 - 2i
To multiply complex numbers, use the FOIL method (First, Outer, Inner, Last), similar to multiplying binomials. (3 * 2) + (3 * -4i) + (5i * 2) + (5i * -4i) = 6 - 12i + 10i - 20i². Remember that i² = -1. So, the expression becomes 6 - 2i - 20(-1) = 6 - 2i + 20. Combining the real parts gives 26 - 2i.
Question 5: In a manufacturing process, the failure rate of a specific component follows a geometric progression. The probability of failure in the first hour is 0.5, in the second hour is 0.25, in the third hour is 0.125, and so on. What is the total probability that the component will fail within the first 5 hours?
- 0.9375
- 0.96875 (Correct answer)
- 0.984375
- 1.0
Correct answer: 0.96875
This is a finite geometric series with first term a = 0.5, common ratio r = 0.5, and n = 5 terms. The sum of a finite geometric series is given by the formula S_n = a(1 - rⁿ) / (1 - r). Plugging in the values: S₅ = 0.5(1 - 0.5⁵) / (1 - 0.5). This simplifies to S₅ = 0.5(1 - 0.03125) / 0.5. The 0.5 in the numerator and denominator cancel, leaving S₅ = 1 - 0.03125 = 0.96875.
Question 6: Given Matrix A = [[3, 1], [4, 2]] and Matrix B = [[5, 0], [1, 6]], what is the product A * B?
- [[15, 0], [4, 12]]
- [[16, 6], [22, 12]] (Correct answer)
- [[15, 6], [20, 12]]
- [[8, 1], [5, 8]]
Correct answer: [[16, 6], [22, 12]]
To find the element in the first row, first column of the product matrix, multiply the elements of the first row of A by the corresponding elements of the first column of B and sum them: (3*5 + 1*1) = 16. For the first row, second column: (3*0 + 1*6) = 6. For the second row, first column: (4*5 + 2*1) = 22. For the second row, second column: (4*0 + 2*6) = 12. The resulting matrix is [[16, 6], [22, 12]].
