`a)` `3(2x - 1)^3 - 1^2020 = 5 . 4^2`
`3(2x - 1)^3 - 1^2020 = 5 . 16`
`3(2x - 1)^3 - 1 = 80`
`3(2x - 1)^3 = 80 + 1`
`3(2x - 1)^3 = 81`
`(2x - 1)^3 = 81 : 3`
`(2x - 1)^3 = 27`
`(2x - 1)^3 = 3^3`
`=>` `2x - 1 = 3`
`=>` `2x = 4`
`=>` `x = 4 : 2`
`=>` `x = 2`
`b)` `5^{x + 1} - 5^x = 500`
`5^x . 5^1 - 5^x = 500`
`5^x . (5^1 - 1) = 500`
`5^x . 4 = 500`
`5^x = 500 : 4`
`5^x = 125`
`x = 3`
`c)` `(3 . x - 2)^3 = 2 . 32`
`(3 . x - 2)^3 = 64`
`(3 . x - 2)^3 = 4^3`
`3 . x - 2 = 4`
`3 . x = 4 + 2`
`3 . x = 6`
`x = 2`
`d)` `(x + 1) + (x + 2) + ....... + (x + 30) = 795`
`(x + x + x + ..... + x) + (1 + 2 + 3 + ...... + 30) = 795`
`SSH = (30 - 1) : 1 + 1 = 30`
Tổng = `(30 + 1) . 30 : 2 = 465`
`x . 30 + 465 = 795`
`x . 30 = 795 - 465`
`x . 30 = 330`
`x = 330 : 30`
`x = 11`