Tìm x,biết :
a) (2x-4)4= 81 b) (x-1)5= 32 c) (2x-1)6 = (2x-1)
Mình cần gấp,cảm ơn
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\(\left(2x-4\right)^4=81\)
\(\left(2x-4\right)^4=3^4\)
\(\Rightarrow2x-4=3\)
\(\Rightarrow2x=7\)
\(\Rightarrow x=\frac{7}{2}\)
vay \(x=\frac{7}{2}\)
\(\left(x-1\right)^5=-32\)
\(\left(x-1\right)^5=\left(-2\right)^5\)
\(\Rightarrow x-1=-2\)
\(\Rightarrow x=-1\)
vay \(x=-1\)
\(\left(2x-1\right)^6=\left(2x-1\right)^8\)
\(\left(2x-1\right)^6-\left(2x-1\right)^8=0\)
\(\left(2x-1\right)^6-\left(2x-1\right)^6.\left(2x-1\right)^2=0\)
\(\left(2x-1\right)^6.\left[1-\left(2x-1\right)^2\right]=0\)
\(\left(2x-1\right)^6\left(1-2x+1\right)\left(1+2x-1\right)=0\)
\(\left(2x-1\right)^6\left(-2x+2\right)\left(2x\right)=0\)
\(\Rightarrow\left(2x-1\right)^6=0\)hoac \(\Rightarrow\orbr{\begin{cases}-2x+2=0\\2x=0\end{cases}}\)
\(\Rightarrow2x-1=0\) hoac \(\Rightarrow\orbr{\begin{cases}x=1\\x=0\end{cases}}\)
\(\Rightarrow x=\frac{1}{2}\)hoac \(\orbr{\begin{cases}x=1\\x=0\end{cases}}\)
a. (2x-1)4=81
=>(2x-1)4=34
=>2x-1=3
=>2x=3+1
=>2x=4
=>x=4:2
=>x=2
b.(x-1)5=-32
=>(x-1)5=(-2)5
=>x-1=-2
=>x=-2+1
=>x=-1
c.(2x-1)6=(2x-1)8
mà chỉ có: (-1)6=(-1)8; 06=08; 16=18
=> để (2x-1) \(\in\){-1;0;1} thì x \(\in\){0; 1/2; 1}
Bài 2:
a: Ta có: \(2^{x+1}\cdot3^y=12^x\)
\(\Leftrightarrow2^{x+1}\cdot3^y=2^{2x}\cdot3^x\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+1=2x\\x=y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=1\end{matrix}\right.\)
\(2x^4-x^3+2x^2+1=2x^4-2x^3+2x^2+x^3-x^2+x+x^2-x+1\\ \)
\(=2x^2\left(x^2-x+1\right)+x\left(x^2-x+1\right)+\left(x^2-x+1\right)=\left(x^2-x+1\right)\left(2x^2+x+1\right)\)
Vậy a = 2; b = 1; c = 1.
a)5-2x=3x+20
5=3x+20+2x
5=5x+20
=>5x+20=5
5x=5-20
5x=-15
x=(-15):5
x=-3
hoc moi lop 5