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電子課本網(wǎng) 第10頁(yè)

第10頁(yè)

信息發(fā)布者:
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解:?$(2)$?因?yàn)?$(\frac {5}{4})^3=\frac {5}{4}×\frac {5}{4}×\frac {5}{4}=\frac {125}{64},$?
?$(\frac {4}{5})^{-3}=\frac {1}{(\frac {4}{5})^3}=\frac {1}{\frac {4}{5}×\frac {4}{5}×\frac {4}{5}}=\frac {5}{4}×\frac {5}{4}×\frac {5}{4}=\frac {125}{64},$?
所以?$(\frac {5}{4})^3=(\frac {4}{5})^{-3}。$?
?$(4)①(\frac {3}{8})^{-4}=(\frac {8}{3})^4,$?
所以原式?$=(\frac {8}{3})^4×(\frac {3}{4})^4=(\frac {8}{3}×\frac {3}{4})^4=2^4=16;$?
?$ ②(-\frac {1}{2})^{-3}×2^{-4}-4^{-2}×(-0.25)^{-3}$?
?$=(-2)^3×(\frac {1}{2})^4-(\frac {1}{4})^2×(-4)^3$?
?$ =[(-2)×\frac {1}{2}]^3×\frac {1}{2}-[\frac {1}{4}×(-4)]^2×(-4)$?
?$ =-\frac {1}{2}-(-4)$?
?$ =-\frac {1}{2}+4$?
?$ =3\frac {1}{2}$?
解:?$①$?當(dāng)?$2x + 3 = 1$?時(shí),解得?$x = -1,$?
此時(shí)?$x + 2024 = 2023,$?
則?$(2x + 3)^{x + 2024}=1^{2023}=1,$?
所以?$x = -1;$?
?$ ②$?當(dāng)?$2x + 3 = -1$?時(shí),解得?$x = -2,$?
此時(shí)?$x + 2024 = 2022,$?
則?$(2x + 3)^{x + 2024}=(-1)^{2022}=1,$?
所以?$x = -2;$?
?$ ③$?當(dāng)?$x + 2024 = 0$?時(shí),?$x = -2024,$
?此時(shí)?$2x + 3 = -4045,$
?則?$(2x + 3)^{x + 2024}=(-4045)^0=1,$?
所以?$x = -2024。$?
綜上所述,當(dāng)?$x = -1$?或?$x = -2$?或?$x = -2024$?時(shí),
代數(shù)式?$(2x + 3)^{x + 2024}$?的值為?$1。$?
解:設(shè)?$S = 1 + 3^{-1} + 3^{-2} + … + 3^{-1000},$?
?$ $?所以?$3S = 3×(1 + 3^{-1} + 3^{-2} +…+ 3^{-1000}) $?
?$= 3 + 1 + 3^{-1} + 3^{-2} +… + 3^{-999},$?
?$ $?所以?$2S=(3 + 1 + 3^{-1} + 3^{-2} + … + 3^{-999})-$?
?$(1 + 3^{-1} + 3^{-2} + … + 3^{-1000}) $?
?$= 3 - 3^{-1000},$?
?$ $?所以?$S=\frac {3 - 3^{-1000}}{2}。$?

$1 - 2^{-n}$