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\(\frac{2.6^9-2^5.18^4}{2^6.6^8}=\frac{2^{10}.3^9-2^9.3^8}{2^{14}.3^8}=\frac{2^9.3^8.\left(6-1\right)}{2^{14}.3^8}=\frac{5}{2^5}=\frac{5}{32}\)
= 2.29.39-25.24.34.34/ 26.38.28
=210.39-29.38/ 214.38
=29.38.(2.3-1.1)/214.38
=5/32
\(\dfrac{4^5.9^4-2.6^9}{2^{10}.3^8-6^8.20}=\dfrac{\left(2^2\right)^5.\left(3^2\right)^4-2.2^9.3^9}{2^{10}.3^8-3^8.2^8.2^2.5}\\ =\dfrac{2^{10}.3^8-2^{10}.3^9}{2^{10}.3^8-3^8.2^{10}.5}=\dfrac{2^{10}.3^8\left(1-3\right)}{2^{10}.3^8\left(1-5\right)}=\dfrac{-2}{-4}=\dfrac{2}{4}=\dfrac{1}{2}\)
\(\dfrac{4^5.9^4-2.6^9}{2^{10}.3^8-6^8.20}=\dfrac{\left(2^2\right)^5.\left(3^2\right)^4-2.2^9.3^9}{2^{10}.3^8-3^8.2^8.2^2.5}\)
\(=\dfrac{2^{10}.3^8-2^{10}.3^9}{2^{10}.3^8-3^8.2^{10}.5}=\dfrac{2^{10}.3^8\left(1-3\right)}{2^{10}.3^8\left(1-5\right)}=\dfrac{2}{4}=\dfrac{1}{2}\)
Chúc bạn học tốt!
\(B=1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}\)
\(B=1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}-2.\left(\frac{1}{2}+\frac{1}{4}+...+\frac{1}{100}\right)\)
\(B=1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{100}-\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{50}\right)\)
\(B=\frac{1}{51}+\frac{1}{52}+...+\frac{1}{100}\)
\(B< \frac{1}{60}+\frac{1}{60}+...+\frac{1}{60}\)
\(B< \frac{50}{60}\Leftrightarrow B< \frac{5}{6}\)