ƚ ^ C .  &@) & MathType-@@@> Times New Roman؟ww w f'-2 '2y2 '2y2 2y2 2yTimes New Roman؟ww w f'-2 Z4y2 Z4yTimes New Roman؟ww w f'-2 yy2 2xy2 yy2 2xy & "System' f' !-