1.Tìm x
a) (-3)^x / 81=-27
Tìm x
( x+1/3)+(x+1/9)+(x+1/27)+(x+1/81)=56/81
ta có :
\(\frac{x+1}{3}+\frac{x+1}{9}+\frac{x+1}{27}+\frac{x+1}{81}=\left(x+1\right)\times\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)\)
\(=\left(x+1\right)\times\frac{40}{81}=\frac{56}{81}\text{ nên }x+1=\frac{56}{40}=\frac{7}{5}\)
vậy \(x=\frac{7}{5}-1=\frac{2}{5}\)
Tìm x:
( x+1/3) + (x+1/9)+(x+1/27)+(x+1/81) = 56/81
tìm x thuộc N biết:
a) 3\(^{a+1}\)=81
b)( x-1)\(^3\)=27
a) \(3^{a+1}=81\)
\(3^{a+1}=3^4\)
\(a+1=4\)
\(a=3\)
b) \(\left(x-1\right)^3=27\)
\(\left(x-1\right)^3=3^3\)
\(x-1=3\)
\(x=4\)
\(a,3^{a+1}=81\\ \Rightarrow3^{a+1}=3^4\\ \\ \Rightarrow a+1=4\\ \Rightarrow a=3.\\ b,\left(x-1\right)^3=27\\ \Rightarrow\left(x-1\right)^3=3^3\\ \Rightarrow x-1=3\\ \Rightarrow x=4.\)
tìm x thuộc z
(-1/27)^x+1=(1/81)^3
Tìm x:
a) (3/5)^5 * x = (3/7)^7
b) (-1/3)^3 * x = 1/81
c) (x - 1/2)^3 = 1/27
d) (x+1/2)^4 = 16/81
a)\(\left(\frac{3}{5}\right)^5\times x=\left(\frac{3}{7}\right)^7\)
\(\Leftrightarrow\frac{3^5}{5^5}\times x=\frac{3^7}{7^7}\)
\(\Leftrightarrow x=\frac{3^7}{7^7}:\frac{3^5}{5^5}\)
\(\Leftrightarrow x=\frac{3^7\times5^5}{7^7\times3^5}\)
\(\Leftrightarrow x=\frac{3^2\times5^5}{7^7}\)
b)\(\left(\frac{-1}{3}\right)^3\times x=\frac{1}{81}\)
\(\Leftrightarrow\frac{\left(-1\right)^3}{3^3}\times x=\frac{1}{3^4}\)
\(\Leftrightarrow x=\frac{1}{3^4}:\frac{-1}{3^3}\)
\(\Leftrightarrow x=\frac{1\times3^3}{3^4\times\left(-1\right)}\)
\(\Leftrightarrow x=\frac{1}{-3}\)
c)\(\Leftrightarrow\left(x-\frac{1}{2}\right)^3=\left(\frac{1}{3}\right)^3\)
\(\Leftrightarrow x-\frac{1}{2}=\frac{1}{3}\)
\(\Leftrightarrow x=\frac{1}{3}+\frac{1}{2}\)
\(\Leftrightarrow x=\frac{5}{6}\)
d)\(\Leftrightarrow\left(x+\frac{1}{2}\right)^4=\left(\frac{2}{3}\right)^4\)
\(\Leftrightarrow x+\frac{1}{2}=\frac{2}{3}\)
\(\Leftrightarrow x=\frac{2}{3}-\frac{1}{2}\)
\(\Leftrightarrow x=\frac{1}{6}\)
Tìm x: x+1+\(\dfrac{1}{3}\)+\(\dfrac{1}{9}\)+\(\dfrac{1}{27}\)+\(\dfrac{1}{81}\)=2
\(x+\dfrac{40}{27}=2\)
\(x=\dfrac{14}{27}\)
\(x+1+\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{81}=2\)
\(\Leftrightarrow x+\dfrac{121}{81}=2\)
hay \(x=\dfrac{41}{81}\)
Tìm x;
(-3/4)2n -1=81/ 256
27 < 813 :3x < 243
a) \(\left(\frac{-3}{4}\right)^{2n-1}=\frac{81}{256}\Leftrightarrow\left(\frac{-3}{4}\right)^{2n-1}=\left(\frac{-3}{4}\right)^4\)
<=>2n-1=4
<=>2n=5
<=>n=5/2
b)\(27
Tìm x
a. x/15=2/5
b. 3/x-7=27/135
c. 3/4:x + 1/2:1/4=4
a: x=2/5*15=6
b: =>x-7=15
=>x=22
c: =>3/4:x+1/2*4=4
=>3/4:x=4-2=2
=>x=3/8
Tìm số dư khi f(x) = x^81+x^27 + x^9 + x^3 + x chia cho x - 1