Q: The mathematical problem involves calculating the ratio of currents in an electrical transformer using the transformer equations, specifically the turns ratio and impedance relationships.

Answer: The ratio of the secondary to primary current is $\frac{I_{2}}{I_{1}} = \frac{Z_{1}E_{2}^{2}}{Z_{2}E_{1}^{2}} = \frac{4n}{(1 + n)^{2}}$. Explanation: This problem applies the principles of transformer theory, including the relationships between voltages, currents, and impedances. It uses the concept that the current ratio is inversely proportional to the turns ratio, adjusted by the impedance and voltage relationships. The derivation involves the use of the transformer equations and the concept of impedance transformation. Steps: Transformer voltage and current relationships: \[ n = \frac{c}{v} = \frac{\sqrt{\frac{\mu \varepsilon}{\mu_{o} \varepsilon_{o}}}} = \frac{Z(\text{vacuum})}{Z(\text{dielectric})} \] The ratio of the number of turns $n$ relates to the voltage and impedance ratios. Current ratio in terms of impedance and voltage: \[ \frac{I_{r}}{I_{i}} = \left(\frac{E_{r}}{E_{i}}\right)^{2} = \left(\frac{1 - n}{1 + n}\right)^{2} \] This is derived from the transformer equations, considering the voltage transformation ratio. Expressing the ratio of currents: \[ \frac{I_{1}}{I_{i}} = \frac{Z_{i}E_{t}^{2}}{Z_{t}E_{i}^{2}} = \frac{4n}{(1 + n)^{2}} \] where $Z_{i}$ and $Z_{t}$ are the impedances, and $E_{t}$ is the voltage. Final expression: \[ \frac{I_{2}}{I_{1}} = \frac{Z_{i}E_{t}^{2}}{Z_{t}E_{i}^{2}} = \frac{4n}{(1 + n)^{2}} \] This relates the secondary current to the primary current, scaled by the impedance and voltage ratios. Summary: The key concepts involved are the transformer equations, impedance transformation, and the relationships between voltage, current, and impedance ratios in an ideal transformer. The derivation uses algebraic manipulation of these relationships to arrive at the expression for the current ratio.

Q: The direct answer is:

The expression simplifies to the inequality: \[ \left| X \right| \leq \sqrt{E \left[ \left| X \right|^2 \right]} \] which is a form of the Cauchy-Schwarz inequality. Explanation: This derivation shows the application of the Cauchy-Schwarz inequality in the context of random variables or vectors. The inequality bounds the absolute value of the expected value of a product by the product of the square roots of the expected values of the squares, which is a fundamental result in probability and linear algebra. Step-by-step working: The initial expression involves the norm of a linear transformation of a vector $X$, expressed as: \[ |X| \leq \left( \mathbb{E} \left[ |X|^2 \right] \right)^{1/2} \] The derivation uses the fact that: \[ \left| \mathbb{E} [X] \right| \leq \left( \mathbb{E} [|X|^2] \right)^{1/2} \] which is the Cauchy-Schwarz inequality applied to the expectation. The sum notation indicates the summation over components, with $\lambda_i$ being weights or coefficients, and the variance terms $\sigma_i^2(x)$ representing the variance of the components. The inequality ultimately bounds the absolute value of the expectation by the square root of the sum of variances divided by the variance of $X$: \[ \left| \mathbb{E}[X] \right| \leq \sqrt{\frac{n}{\sigma^2_{X}(X)}} \] Conclusion: The key takeaway is that the magnitude of the expected value of $X$ is bounded by the standard deviation (square root of variance), which is a core concept in probability theory and statistics.

Question

The correct answer is: **C. 2**

Accepted Answer

Explanation:  Let's evaluate the expression step-by-step:

Expression: $ 9 - 3 \div \frac{1}{3} + 1 $

Order of operations (PEMDAS/BODMAS):

Division  
Subtraction and addition (left to right)

Steps:

Calculate $ 3 \div \frac{1}{3} $:

$\div \frac{1}{3}$ is equivalent to multiplying by 3:  $$ 3 \times 3 = 9 $$

Now substitute back into the expression:

$$ 9 - 9 + 1 $$

Perform subtraction:

$$ 9 - 9 = 0 $$

Perform addition:

$$ 0 + 1 = 1 $$

However, the options do not include 1, so let's recheck the calculation:

Actually, the initial step should be:

$ 3 \div \frac{1}{3} = 3 \times 3 = 9 $

So, the expression becomes:

$$ 9 - 9 + 1 = 1 $$

But since 1 is not an option, let's verify the options again. The options are:  A. 1  B. 3  C. 2  D. 9  E. ---

The calculation yields 1, which matches option A.

Correction: The initial answer should be A. 1.

Final answer: A. 1

Note: The initial quick answer was incorrect; the correct choice based on the calculation is A. 1.