Đáp án+Giải thích các bước giải:
`1)(-5/6)^{12} .x=(-5/6)^{14}`
`-> x=(-5/6)^{14} :(-5/6)^{12}`
`-> x=(-5/6)^2`
`-> x=25/36`
Vậy `x=25/36`
`2)(x-2/5)^2=4/9`
`-> x-2/5=± 2/3`
`->` \(\left[ \begin{array}{l}x-\dfrac{2}{5}=\dfrac{2}{3}\\x-\dfrac{2}{5}=\dfrac{-2}{3}\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=\dfrac{16}{15}\\x=\dfrac{-4}{15}\end{array} \right.\)
Vậy `x ∈{16/15;-4/15}`
`3)(x+2/3)^3=(-64)/27`
`->(x+2/3)^3=(-4/3)^3`
`-> x+2/3=-4/3`
`-> x=-4/3-2/3`
`-> x=-6/3`
`-> x=-2`
Vậy `x=-2`
`4)81/3^x=3`
`-> 3^x=81:3`
`-> 3^x=27`
`-> 3^x=3^3`
`-> x=3`
Vậy `x=3`
`5)27^8 .x=9^{14}`
`->(3^3)^8.x=(3^2)^{14}`
`-> 3^{24} .x=3^{28}`
`-> x=3^{28} :3^{24}`
`-> x=3^4`
`->x=81`
Vậy `x=81`
`6)2^{x+2}+2^x=80`
`->2^x .2^2 +2^x=80`
`-> 2^x (2^2+1)=80`
`-> 2^x .5=80`
`-> 2^x=16`
`-> 2^x=2^4`
`-> x=4`
Vậy `x=4`
