If $x = A \cos 4t + B \sin 4t$,then $\frac{d^2x}{dt^2} = $

Let $g(x) = \log(f(x))$ where $f(x)$ is a twice differentiable positive function on $(0, \infty)$ such that $f(x+1) = x f(x)$. Then,for $N = 1, 2, 3, \ldots$,$g^{\prime \prime}\left(N+\frac{1}{2}\right) - g^{\prime \prime}\left(\frac{1}{2}\right) = $

If $y = a \sin x + (5 + 2x) \cos x$,then $y'' + y =$

If $y = x + e^x$,then at $x = 1$,$\frac{d^2x}{dy^2}$ is equal to

Suppose the function $f(x) - f(2x)$ has the derivative $5$ at $x = 1$ and derivative $7$ at $x = 2$. The derivative of the function $f(x) - f(4x)$ at $x = 1$ has the value equal to:

If $y = a{x^{n + 1}} + b{x^{ - n}}$,then ${x^2}\frac{{{d^2}y}}{{d{x^2}}} = $