>>720
単に公式に当てはめればいい

$data = import-csv "csvのパス" -Header X,Y

$meanX = $data.X | measure -Average | select -expand Average
$meanY = $data.Y | measure -Average | select -expand Average

$sd = $data | foreach { ($_.X - $meanX) * ($_.X - $meanX) } | measure -Average | select -expand Average
$cd = $data | foreach { ($_.X - $meanX) * ($_.Y - $meanY) } | measure -Average | select -expand Average
$slope = $cd / $sd

$meanY - $slope * $meanX