Solve the following:

$($i$)y^{\text{'}\text{'}\text{'}}=e^{-0\mathrm{.}2x}$

$($ii$)y^{\text{'}}=se{c}^{2}y$

$($iii$)\frac{dr}{dt}=-2tr$;$r(0)=r_0$

$($iv$)y^{\text{'}}=(x+y-2{)}^2$;$y(0)=2$

$($v$)x{y}^{\text{'}}=x+y$