What is the formula for calculating double$-$declining$-$balance depreciation?

$($Cost $-$ Accumulated depreciation$)(2/$useful life$)$

$($Cost $-$ Reslduat value$)($actual production this' periodiestimated total production$)$

$($Cost $-$ Accumulated depreciation$)/(2$ useful life$)$

$($Cost$-$Reslduar value$)($thusefur The$)$