Find the higher order ($2$) derivative of $b^2x^2+a^2y^2$

Find the derivative

$\frac{d^3}{dx^3}\left(x\cdot\cos\left(x\right)\right)$

Find the derivative

$\frac{d^2}{dx^2}\left(\left(1-x^2\right)\cdot\cos\left(x\right)\right)$

Find the derivative

$\frac{d^{\left(4\right)}}{dx^{\left(4\right)}}\left(x^4\cdot\ln\left(x\right)\right)$

Find the derivative

$\frac{d^{\left(7\right)}}{dx^{\left(7\right)}}\left(x^6\cdot\ln\left(x\right)\right)$

Find the derivative

$\frac{d^2}{dx^2}\left(\cos^2\left(x\right)\right)$

Find the derivative

$\frac{d^2}{dx^2}\left(sen\left(x\right)\right)$

Find the derivative

$\frac{d^2}{dx^2}\left(x^3\right)$