Question

The differential equation obtained on eliminating A and B from y = A cos (wt) + B sin (wt) is –

• A. y¢¢ + y¢ = 0
• B. y¢¢ – w²y = 0
• C. y¢¢ = – w²y
• D. y¢¢ + y = 0

Answer 1

Answer: (C)

y¢¢ = – w²y

Answer 2

y = A cos wt + B sin wt

y¢ = Aw (– sin wt) + Bw cos wt

y¢¢ = – Aw²cos wt –Bw² sin wt

y¢¢ = –w²y