Receivables for which formal instruments of credit (documents) are issued as proof of the debt are called: a. accounts receivable. b. interest receivable. c. notes receivable. d. other receivables. A change in the estimated useful life of equipment requires: a. a change in the amount of depreciation recognized in previous years. b. that no change be made in the periodic depreciation so that depreciation amounts are comparable over the life of the asset. c. that amount of periodic depreciation be changed in the current year and in future years. d. that income for the current year be increased. All of the following are intangible assets except. a. copyrights. b. goodwill. c. patents. d. research and development costs