Question

If y=a sin 3x+ b cos 3x and $\frac{d^{2} y }{dx^{2} }$ = ky, then what is the value of k?
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Answer 1

Step-by-step explanation:

You have to do first and second derivatives :

y = a sin 3x + b cos 3x

dy/dx = 3a cos 3x - 3b sin 3x

d²y/dx² = - 9a sin 3x - 9b cos 3x

Next, you have to compare it :

let d²y/dx² = ky,

-9a sin 3x - 9b cos 3x = k(a sin 3x + b cos 3x)

-9(a sin 3x + b cos 3x) = k(a sin 3x + b cos 3x)

Therefore, k is equals to 9.