Tìm x biết:
a,\(\frac{x^7}{81}=27\) b,\(\frac{x^8}{9}=729\)
Tìm x,biết:
a) \(\frac{x^7}{81}\) = 27
b) \(\frac{x^8}{9}\) 729
a) Ta có: \(\frac{x^7}{81}=27\)
\(\Rightarrow x^7=27.81=2187\)
Mà \(2187=3^7\) \(\Rightarrow x^7=3^7\Leftrightarrow x=3\)
Vậy x = 3
b) Ta có: \(\frac{x^8}{9}=729\)
\(\Rightarrow x^8=729.9=6561\)
Mà \(6561=3^8\) \(\Rightarrow x^8=3^8\Leftrightarrow x=3\)
Vậy x = 3
CHÚC BẠN HỌC TỐT
\(\frac{x^7}{81}=27\Rightarrow27.81=x^7\Rightarrow x=3\)
\(\frac{x^8}{9}=729\Rightarrow x^8=729.9\Rightarrow x=3\)
tíc mình
nha
\(a.\)\(\frac{x^7}{81}=27\)
\(\Rightarrow x^7=27.81\)
\(\Leftrightarrow x^7=2187\)
\(\Leftrightarrow x^7=3^7\)
\(\Leftrightarrow x=3\)
\(b.\)\(\frac{x^8}{9}=729\)
\(\Rightarrow x^8=729.9\)
\(\Leftrightarrow x^8=6561\)
\(\Leftrightarrow x^8=3^8\)
\(\Leftrightarrow x=3\)
Vậy : Ở cả 2 câu x đều bằng 3 nhé.
~ Rất vui vì giúp đc bn ~
a) \(\left(2x+3\right)^2=\frac{9}{144}\)
\(\Leftrightarrow\left(2x+3\right)^2=\left(\frac{1}{4}\right)^2=\left(-\frac{1}{4}\right)^2\)
\(\Rightarrow\orbr{\begin{cases}2x+3=\frac{1}{4}\\2x+3=\frac{-1}{4}\end{cases}\Leftrightarrow\orbr{\begin{cases}2x=\frac{-11}{4}\\2x=\frac{-13}{4}\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{-11}{8}\\x=\frac{-13}{8}\end{cases}}}\)
Vậy ...
b) Ta có: \(\left(3x-1\right)^3=\frac{-8}{27}=\left(\frac{-2}{3}\right)^3\)
\(\Leftrightarrow3x-1=\frac{-2}{3}\Leftrightarrow3x=\frac{1}{3}\Leftrightarrow x=\frac{1}{9}\)
Vậy ....
c) \(x^{10}=25x^8\Leftrightarrow x^{10}:x^8=25\Leftrightarrow x^2=25\Leftrightarrow x=\left\{5;-5\right\}\)
Vậy ...
d) \(\frac{x^7}{81}=27\Leftrightarrow x^7=27.81=2187\)
Mà 37 = 2187 => x7 = 37 => x = 3
Vậy ....
e) \(\frac{x^8}{9}=729\Leftrightarrow x^8=729.9=6561\)
Mà 38 = (-3)8 = 6561
=> x8 = 38 = (-3)8
=> x = {-3;3}
Vậy ...
Tìm x, biết:
a, x^7/81 = 27
b, x^8/9 = 729
a) \(\frac{x^7}{81}=27\)
=> x7 = 27.81
=> x7 = 33.34
=> x7 = 37
=> x = 3
Vậy x = 3
b) \(\frac{x^8}{9}=729\)
=> x8 = 729.9
=> x8 = 36.32
=> x8 = 38 = (-3)8
=> \(x\in\left\{3;-3\right\}\)
Vậy \(x\in\left\{3;-3\right\}\)
tìm x biết : a,\(\frac{x^7}{81}=27\); b,\(\frac{x^8}{9}=729\); c.\(^{\left[x-\frac{1}{2}\right]^0}\); d,\(\left[X-2\right]^2=1\); e, \(\left[2X-1\right]^3=8\); f,\(\left[X+\frac{1}{2}\right]^2\)=\(\frac{1}{16}\)
Tìm x, biết:
a)\(x.\frac{{14}}{{27}} = \frac{{ - 7}}{9}\)
b)\(\left( {\frac{{ - 5}}{9}} \right):x = \frac{2}{3};\)
c)\(\frac{2}{5}:x = \frac{1}{{16}}:0,125\)
d)\( - \frac{5}{{12}}x = \frac{2}{3} - \frac{1}{2}\)
a)
\(\begin{array}{l}x.\frac{{14}}{{27}} = \frac{{ - 7}}{9}\\x = \frac{{ - 7}}{9}:\frac{{14}}{{27}}\\x = \frac{{ - 7}}{9}.\frac{{27}}{{14}}\\x = \frac{{ - 3}}{2}\end{array}\)
Vậy \(x = \frac{{ - 3}}{2}\).
b)
\(\begin{array}{l}\left( {\frac{{ - 5}}{9}} \right):x = \frac{2}{3}\\x = \left( {\frac{{ - 5}}{9}} \right):\frac{2}{3}\\x = \left( {\frac{{ - 5}}{9}} \right).\frac{3}{2}\\x = \frac{{ - 5}}{6}\end{array}\)
Vậy \(x = \frac{{ - 5}}{6}\).
c)
\(\begin{array}{l}\frac{2}{5}:x = \frac{1}{{16}}:0,125\\\frac{2}{5}:x = \frac{1}{{16}}:\frac{1}{8}\\\frac{2}{5}:x = \frac{1}{{16}}.8\\\frac{2}{5}:x = \frac{1}{2}\\x = \frac{2}{5}:\frac{1}{2}\\x = \frac{2}{5}.2\\x = \frac{4}{5}\end{array}\)
Vậy \(x = \frac{4}{5}\)
d)
\(\begin{array}{l} - \frac{5}{{12}}x = \frac{2}{3} - \frac{1}{2}\\ - \frac{5}{{12}}x = \frac{4}{6} - \frac{3}{6}\\ - \frac{5}{{12}}x = \frac{1}{6}\\x = \frac{1}{6}:\left( { - \frac{5}{{12}}} \right)\\x = \frac{1}{6}.\frac{{ - 12}}{5}\\x = \frac{{ - 2}}{5}\end{array}\)
Vậy \(x = \frac{{ - 2}}{5}\).
Chú ý: Khi trình bày lời giải bài tìm x, sau khi tính xong, ta phải kết luận.
Tìm X biết : x^7/81 = 27. x^8/9 = 729
x^7/81 = 27 x^8/9 = 729
x^7 : 81= 27 x^8 : 9 = 729
x^7 =27.81 x^8 = 729.9
x^7 =2187 x^8 =6561
x^7 = 3^7 x^8 = 3^8
=> x =3 => x = 3
\(\frac{x^7}{81}=27\Rightarrow x^7=27.81=2187\Rightarrow x=\sqrt[7]{2187}=3\)
\(\frac{x^8}{9}=729\Rightarrow x^8=729.9=6561\Rightarrow x=\sqrt[8]{6561}=3\)
\(\frac{x^7}{81}=27\)
\(\Rightarrow x^7.1=81.27\)
\(\Rightarrow x^7=2187\)
Ta thấy : \(3^7=2187\)
\(\Rightarrow x=\sqrt[7]{2187}=3\)
\(\frac{x^8}{9}=729\)
\(\Rightarrow x^8.1=729.9\)
\(\Rightarrow x^8=6561\)
\(\Rightarrow x=\sqrt[8]{6561}=3\)
Bài tập bổ sung 7 : Tìm x , biết :
a. x mũ 7 / 81 = 27
b. x mũ 8 / 9 = 729
\(\frac{x^7}{81}=27\Rightarrow x^7=27.81\Rightarrow x^7=3^3.3^4\Rightarrow x^7=3^7\Rightarrow x=3\)
\(\frac{x^8}{9}=729\Rightarrow x^8=729.9\Rightarrow x^8=3^6.3^2\Rightarrow x^8=3^8\Rightarrow x=3\)
1. Tìm x\(\inℚ\), biết:
a)\(\left(x-\frac{1}{2}\right)2=0\)
b)\(\left(x-2\right)^2=1\)
c) \(\left(2x-1\right)^3=-8\)
d)\(\left(x+\frac{1}{2}\right)^2=\frac{1}{16}\)
e)\(\frac{x^7}{81}=27\)
g)\(\frac{x^8}{9}=^{729}\)
x^7/81 = 27
x^8/9= 729
\(\frac{x^7}{81}\) = 27
x7 : 81 = 27
x7 = 27 . 81 = 33 . 34
x7 = 37
Suy ra : x = 3
Bài 2 :
\(\frac{x^8}{9}\) = 729
x8 : 9 = 729
x8 = 729 . 9
x8 = 36 . 32
x8 = 38
Suy ra : x = 3