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SSC Applied Mathematics QUESTION #4149
Question 1
For $y'' + y = \sec(x)$, using variation of parameters, what is $u_1'$ where $y_p = u_1\cos(x) + u_2\sin(x)$?
  • $-\sin(x)\sec(x)$
  • $-\sin(x)\sec(x) = -\tan(x)$✔️
  • $\cos(x)\sec(x) = 1$
  • $\tan(x)$
Correct Answer Explanation
$u_1' = -\frac{y_2 f(x)}{W} = -\frac{\sin(x) \sec(x)}{1} = -\tan(x)$.