#### Answer

a. $-2sin(x)$,
b. $9cos(x)$,

#### Work Step by Step

Recall the formulas $\frac{d}{dx}(sin(x))=cos(x)$, $\frac{d}{dx}(cos(x))=-sin(x)$,
a. $y'=-2cos(x)$, $y''=2sin(x)$, $y'''=2cos(x)$, $y^{(4)}=-2sin(x)$,
b. $y'=-9sin(x)$, $y''=-9cos(x)$, $y'''=9sin(x)$, $y^{(4)}=9cos(x)$,