Đáp án:
`3) x = 2`
`4) x = 5`
`7) x = 5`
`8) x = 3`
`11) x ∈ { 8 ; - 8 }`
`12) x = 4`
Giải thích các bước giải:
`3)` $5^{x}$ `= 125`
`=>` $5^{x}$ `= 5²`
`=> x = 2`
Vậy `x = 2`
`4)` $2^{x}$ `- 26 = 6`
`=>` $2^{x}$ `= 6 + 26`
`=>` $2^{x}$ `= 32`
`=>` $2^{x}$ `=` $2^{5}$
`=> x = 5`
Vậy `x = 5`
`7) 64 .` $4^{x}$ `=` $4^{8}$
`=>` $4^{3}$ . $4^{x}$ `=` $4^{8}$
`=>` $4^{3+x}$ `=` $4^{8}$
`=> 3 + x = 8`
`=> x = 8 - 3`
`=> x = 5`
Vậy `x = 5`
`8)` $4^{x - 1}$ `= 16 `
`=>` $4^{x - 1}$ `=` $4^{2}$
`=> x - 1 = 2`
`=> x = 2 + 1 `
`=> x = 3`
Vậy `x = 3`
`11) x² = 64`
`=> x² ∈ { 8² ; - 8² }`
`=> x ∈ { 8 ; - 8 }`
Vậy `x ∈ { 8 ; - 8 }`
`12) ( x + 1 )³ = 125`
`=> ( x + 1 )³ =` $5^{3}$
`=> x + 1 = 5`
`=> x = 4`
Vậy `x = 4`
