Explanation:
(a)(i) Trade discount: It is a reduction in the catalogue price of goods in order to encourage buyers to buy in large quantities.
(ii) Cash discount: It is a reduction in the invoice price of goods to encourage prompt payment.
(iii) Bad debts: These are debts which are deemed irrecoverable.
(iv) Provision for doubtful debts: These are estimates of the debts at a point in time which arenot likely to be recovered.
(v) Bad debts recovered: These are debts previously written-off but which have subsequently been retrieved or paid by the debtors.
(b) Errors that do not affect the agreement of the trial balance are:

Error of omission
Error of original entry
Error of commission
Error of principle
Complete reversal of entries
Error of compensation/compensating error
Error of transposition/transposition error
Error of duplication