~ Bạn tham khảo ~
`b, 5^x + 39 = 2^4 xx 4`
`5^x + 39 = 16 xx 6`
`5^x + 39 = 64`
`5^x = 64 - 39`
`5^x = 25`
`=> 5^x = 5^2`
Vậy ` x = 2`
`c, ( x-1)^4 + 3 = 84`
`(x-1)^4 = 84-3`
`(x-1)^4 = 81`
`=> (x-1)^4 = ±3^4`
\(\left[ \begin{array}{l}x-1=3\\x-1=-3\end{array} \right.\)
\(\left[ \begin{array}{l}x=3+1\\x=-3+1\end{array} \right.\)
\(\left[ \begin{array}{l}x=4\\x=-2\end{array} \right.\)
Vậy ` x ∈ { 4 ; -2 }`
