Step 1: Understanding the Concept:
A higher-order ordinary differential equation can be converted into a system of first-order equations by introducing new variables.
Step 2: Key Formula or Approach:
The order of the differential equation is the highest derivative present.
Here, the highest derivative is \(x'''\), which is the third derivative.
So, the order is 3.
A third-order ODE is equivalent to a system of three first-order ODEs.
Step 3: Detailed Explanation:
Let \(x_1 = x\), \(x_2 = x'\), \(x_3 = x''\).
Then,
\[
x_1' = x' = x_2
\]
\[
x_2' = x'' = x_3
\]
\[
x_3' = x''' = -3x'' - 2x' + 5x + \sin 2t = -3x_3 - 2x_2 + 5x_1 + \sin 2t
\]
So, we have three first-order equations.
Thus, the number of first-order equations is 3.
Step 4: Final Answer:
Therefore, option (D) is correct.