2.54: Second derivative identity with a sine combination

0606/22/O/N/19 — Question 2 · 5 marks

Given that y=2sin3x+cos3xy = 2\sin 3x + \cos 3x, show that d2ydx2+dydx+3y=ksin3x\dfrac{\mathrm{d}^{2}y}{\mathrm{d}x^{2}} + \dfrac{\mathrm{d}y}{\mathrm{d}x} + 3y = k\sin 3x, where kk is a constant to be determined.
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