a)Ta có:(9/25)ⁿ=(3/5)⁴=>(9/25)ⁿ=(9/25)²=>n=2

b)(2ⁿ-2)²=16=>2ⁿ-2=4 hoặc 2ⁿ-2= -4=>2ⁿ=6 hoặc 2ⁿ=-2=>không tìm được giá trị của n thỏa mãn

c)(1-n )³=216=>(1-n)³=6³=>1-n=6=>n=-5

dung ko ban 

chọn câu trả lời của mk nha!!!

a/ \(3^x.2^x=216\)

\(\Leftrightarrow\left(3.2\right)^x=216\)

\(\Leftrightarrow6^x=216\)

\(\Leftrightarrow6^x=6^3\)

\(\Leftrightarrow x=3\)

Vậy ......

b/ \(\dfrac{1}{2}\left(x-\dfrac{1}{3}\right)+\dfrac{-1}{2}=\dfrac{3}{4}\)

\(\Leftrightarrow\dfrac{1}{2}\left(x-\dfrac{1}{3}\right)=\dfrac{5}{4}\)

\(\Leftrightarrow x-\dfrac{1}{3}=\dfrac{5}{2}\)

\(\Leftrightarrow x=\dfrac{17}{6}\)

Vậy ..

a)\(x=\left(\dfrac{3}{56}\cdot\dfrac{28}{9}\right):\dfrac{-3}{7}=\dfrac{1}{6}:\dfrac{-3}{7}=-\dfrac{7}{18}\)

b)\(x=\left(\dfrac{7}{15}\cdot\dfrac{5}{3}\right)+\dfrac{3}{16}=\dfrac{7}{9}+\dfrac{3}{16}=\dfrac{139}{144}\)

c)\(x=\left(\dfrac{5}{6}-\dfrac{2}{5}\right).5=\dfrac{13}{6}\)

d)\(=>x\left(\dfrac{3}{4}-\dfrac{2}{5}\right)=\dfrac{1}{6}\cdot\left(\dfrac{3}{7}+\dfrac{5}{7}\right)\)

\(x\cdot\dfrac{7}{20}=\dfrac{4}{21}=>x=\dfrac{4}{21}\cdot\dfrac{20}{7}=\dfrac{80}{147}\)

ok

3^x+2 - 3^x = 216
3^x.3² - 3^x.1 = 216
3^x.(3²-1) = 216
3^x.(9-1)   = 216
3^x.8        = 216
3^x           = 216 : 8
3^x           = 27
3^x           = 3³
  x           = 3
Vậy x = 3

a: x=2/3-4/5=10/15-12/15=-2/15

b: 1/2-x=7/12

=>x=1/2-7/12=-1/12

c: =>7/2:x=-7/2

=>x=-1

d: =>1/6x=3/8-5/2=3/8-20/8=-17/8

=>x=-17/8*6=-102/8=-51/4

e: =>1,5x=-1,5

=>x=-1

(1-x)³=216

(1-x)³=6³

=>1-x=6

x=1-6

x=-5