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Ta có:
\(\left(\frac{-1}{8}\right)^{100}=\frac{\left(-1\right)^{100}}{8^{100}}=\frac{1}{\left(2^3\right)^{100}}=\frac{1}{2^{300}}\)
\(\left(\frac{-1}{4}\right)^{200}=\frac{\left(-1\right)^{200}}{4^{200}}=\frac{1}{\left(2^2\right)^{100}}=\frac{1}{2^{200}}\)
Vì \(2^{300}>2^{200}\)\(\Rightarrow\frac{1}{2^{300}}< \frac{1}{2^{200}}\)
\(\Rightarrow\left(\frac{-1}{8}\right)^{^{100}}< \left(\frac{-1}{4}\right)^{200}\)
ta có:1/8^100
-1/4^200=(-1/4^2)^100=1/16^100
=>1/8^100 >1/16^100
=>1/8^100 >-1/4^200
\(\frac{1}{2}>\frac{1}{3}\\ \Rightarrow\left(\frac{1}{2}\right)^{200}>\left(\frac{1}{3}\right)^{200}\)
Bài làm
Ta có: \(\left(-\frac{1}{4}\right)^2=\left(\frac{1}{4}\right)^2\)
\(\left(\frac{1}{8}\right)^5=\left[\left(\frac{1}{4}\right)^2\right]^5=\left(\frac{1}{4}\right)^{10}\)
Mà \(2< 10\)
=> \(\left(\frac{1}{4}\right)^2< \left(\frac{1}{4}\right)^{10}\)
Hay \(\left(-\frac{1}{4}\right)^2< \left(\frac{1}{8}\right)^5\)
Vậy \(\left(-\frac{1}{4}\right)^2< \left(\frac{1}{8}\right)^5\)
# Học tốt #
Ta có:
\(A=\left(\frac{1}{2^2}-1\right)\left(\frac{1}{3^2}-1\right)\left(\frac{1}{4^2}-1\right)..\left(\frac{1}{2017^2}-1\right)\)
\(A=\left(\frac{1}{4}-1\right)\left(\frac{1}{9}-1\right)\left(\frac{1}{16}-1\right)...\left(\frac{1}{2017^2}-1\right)\)
\(A=\left(-\frac{3}{2^2}\right)\left(\frac{-8}{3^2}\right)\left(\frac{-15}{4^2}\right)...\left(\frac{-\left(1-2017^2\right)}{2017^2}\right)\)
( có 2016 thừa số)
\(A=\frac{3.8.15...\left(1-2017^2\right)}{2^2.3^2.4^2...2017^2}\)
\(A=\frac{\left(1.3\right)\left(2.4\right)...\left(2016.2018\right)}{\left(2.2\right)\left(3.3\right)\left(4.4\right)...\left(2017.2017\right)}\)
\(A=\frac{\left(1.2.3....2016\right)\left(3.4.5....2018\right)}{\left(2.3.4...2017\right)\left(2.3.4...2017\right)}\)
\(A=\frac{1.2018}{2017.2}\)
\(A=\frac{1009}{2017}\)
Ta có : \(\frac{1009}{2017}>0\) (vì tử và mẫu cùng dấu)
\(\frac{-1}{2}< 0\) (vì tử và mẫu khác dấu)
Vậy A>B
bằng nhau
ta có:\(\left(-\frac{1}{8}\right)^{180}=\left(\frac{1}{8}\right)^{180}=\left(\frac{1}{4}\right)^{2^{180}}=\left(\frac{1}{4}\right)^{360}\)
ta có :\(\left(-\frac{1}{4}\right)^{200}=\left(\frac{1}{4}\right)^{200}\)
=>(1/4)^360<(1/4)^200
Vậy : (-1/8)^180 < ( -1/4)^200