تَرْضَى → لَمْ تَرْضَ → اِرْضَ
Translation: You are pleased → You were not pleased → Be pleased.
Form the second-person imperative from the jussive stem: drop the imperfect prefix and, where needed, introduce hamzat al-waṣl. Hence اِرْضَ lacks both the imperfect's initial tāʾ and its final alif.
StepFormOperation
ImperfectتَرْضَىSecond-person prefix tāʾ
JussiveتَرْضَDrop final weak letter
CommandاِرْضَDrop prefix; introduce hamzat al-waṣl
This sequence illustrates the masculine-singular command. Other addressees require their appropriate endings.