Question

why is economical to use ac rather than DC to transfer power​

Answer 1

AC is much easier (therefore cheaper) to step up and down in voltage than DC, and can be done more efficiently (typcially, currently) than the much more expensive and complex DC step-up/step-down systems. ... Over the distances that mains power is transmitted, there are some losses when using AC, but the losses are small.

Answer 2

upside 1 crrctt .............