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The elimination of arbitrary constants \(c_{1}, c_{2}, c_{3}\) and \(c_{4}\) from \(y = (c_{1} + c_{2})\) sin \((x + c_{3}) - c_{4}e^{x}\) gives a differential equation of order

  • A.1
  • B.2
  • C.3
  • D.4
  • E.5

Answer: C

The order is 3.

The order equals the number of independent arbitrary constants. \(c_{1}\) and \(c_{2}\) appear only as the sum \(c_{1} + c_{2}\), which is a single constant A. So the family is \(y = A\sin(x + c_{3}) - c_{4}e^{x}\).

That leaves three independent constants, A, \(c_{3}\) and \(c_{4}\), so eliminating them needs three differentiations and gives a third-order equation. Counting the four letters gives 4, which overlooks that \(c_{1}\) and \(c_{2}\) cannot be separated.

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