`TTT:`
`n_1 = 1650 \text{vòng}`
`n_2 = 270 \text{vòng}`
`U_1 = 220 V`
`b) U_2 = 90 V`
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`a){U_1}/{U_2} = {n_1}/{n_2}`
`=> U_2 = {U_1 . n_2}/{n_1}`
`=> U_2 = {220 . 270}/{1650}`
`=> U_2 = 36 V`
`b) {U_1}/{U_2} = {n_1}/{n_2}`
`=> n_2 = {U_2 . n_1}/{U_1}`
`=> n_2 = {90 . 1650}/{220}`
`=> n_2 = 675 \text{vòng}`