Given that y = 2 sin 3x + cos 3x, show that d²y/dx² + dy/dx + 3y = k sin 3x, where k is a constant to be determined.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.
- B1 dy/dx = 6 cos 3x
- B1 -3 sin 3x
- B1 d²y/dx² = -18sin3x-9cos3x FT Correct derivative of their dy/dx
- M1 Insert and collect like terms Must insert for y, their dy/dx and d²y/dx² correctly resulting in 6 terms.
- A1 k = -15 Allow -15sin3x seen nfww
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