Câu hỏi của Lê Minh

Question

TÌM SỐ TN X BIẾT

a, 2x. 4 = 128

b, x15= x

c, 16x< 128

d,5x. 5x+1. 5x+2< 1000000000000000000 : 218

e,2x. ( 22)2= ( 23) 2

f, ( x5)10=x

Bùi Anh Tuấn · Accepted Answer

$a,2^x\cdot4=128$

$2^x=128:4=32$

$2^x=2^5$

$x=5$

$b,x^{15}=x$

$x^{15}-x=0$

$x\left(x^{14}-1\right)=0$

$\left\{{}\begin{matrix}x=0\x^{14}-1=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\x=1\end{matrix}\right.$

$c,16^x< 128$

$2^{4x}< 2^7$

$4x< 7$

$x=1$

d,$5^x\cdot5^{x+1}\cdot5^{x+2}< 1000000000000000000:2^{18}$

$5^{x+x+1+x+2}< 10^{18}:2^{18}$

$5^{3x+3}< 5^{18}$

$3x+3< 18$

$3\left(x+1\right)< 18$

$x+1< 6$

$x< 5$

$e,2^x\cdot\left(2^2\right)^2=\left(2^3\right)^2$

$2^x\cdot2^4=2^6$

$2^{x+4}=2^6$

$x+4=6$

$x=2$

$f,\left(x^5\right)^{10}=x$

$x^{50}=x$

$x^{50}-x=0$

$x\left(x^{49}-1\right)=0$

$\left\{{}\begin{matrix}x=0\x^{49}-1=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\x=1\end{matrix}\right.$Câu trả lời: $a,2^x\cdot4=128$