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Có: \(\dfrac{5^2.6^9.10+6^5.2^3.15^3}{5^2.6^8.10-2.6^8.10}=\dfrac{5^2.2^9.3^9.2.5+2^5.3^5.2^3.3^3.5^3}{5^2.2^8.3^8.2.5-2.2^8.3^8.2^3.5^3}\)
=\(\dfrac{2^{10}.3^95^3+2^8.3^8.5^3}{2^9.3^8.5^3-2^{12}.3^8.5^3}=\dfrac{2^8.3^8.5^3.\left(12+1\right)}{2^8.3^8.5^3\left(2-16\right)}\)
= \(\dfrac{12+1}{2-16}=\dfrac{-13}{14}\)
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\(=\dfrac{5^2\cdot2^9\cdot3^9\cdot2\cdot5+2^5\cdot2^3\cdot3^5\cdot5^3\cdot3^3}{5^2\cdot2^8\cdot3^8\cdot2\cdot5-2\cdot2^8\cdot3^8\cdot2^3\cdot5^3}\)
\(=\dfrac{5^3\cdot2^{10}\cdot3^9+5^3\cdot2^8\cdot3^8}{5^3\cdot2^9\cdot3^8-5^3\cdot2^{12}\cdot3^8}\)
\(=\dfrac{5^3\cdot2^8\cdot3^8\left(2^2\cdot3+1\right)}{5^3\cdot2^9\cdot3^8\left(1-2^3\cdot1\right)}=\dfrac{1}{2}\cdot\dfrac{13}{1-9}=-\dfrac{13}{16}\)
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25.9-25.17/-8.80-.10=25.(9-17)/-8(80+10)=25.(-8)/-8.90=25/90=5/18
48.12-48.15/-3.270-3.30=48.(12-15)/-3(270+30)=48.-3/-3.300=48/300=4/25
thông cảm e mới học lớp 6 nên sai thì thôi còn chỗ -3 hay -8 là vì thay -2 lần trừ ra cộng
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\(B=\frac{3}{2.4}-\frac{5}{4.6}+\frac{7}{6.8}-\frac{9}{8.10}+...+\frac{2019}{2018.2020}\)
\(B=\frac{3}{2.1.2.2}-\frac{5}{2.2.2.3}+\frac{7}{2.3.2.4}-\frac{9}{2.4.2.5}+...+\frac{2019}{2.1009.2.1010}\)
\(B=\frac{1}{4.}.\left(\frac{3}{1.2}-\frac{5}{2.3}+\frac{7}{3.4}-\frac{9}{4.5}+...+\frac{2019}{1009.1010}\right)\)
\(B=\frac{1}{4.}.\left(\frac{3}{1}-\frac{3}{2}-\frac{5}{2}+\frac{5}{3}+\frac{7}{3}-\frac{7}{4}-\frac{9}{4}+\frac{9}{5}+...+\frac{2019}{1009}-\frac{2019}{1010}\right)\)
\(B=\frac{1}{4.}.\left(\frac{3}{1}-4+4-4+4-...+4-\frac{2019}{1010}\right)\)
\(B=\frac{1}{4.}.\left(\frac{3}{1}-\frac{2019}{1010}\right)=\frac{1011}{4040}\)
\(\frac{5^2.6^9.10+6^5.2^3.15^3}{5^2.6^8.10-2.6^8.10^3}=\frac{5^2.2^9.3^9.2.5+2^5.3^5.2^3.5^3.3^3}{5^2.2^8.3^8.2.5-2.2^8.3^8.2^3.5^3}\)
\(=\frac{2^{10}.3^9.5^3+2^8.3^8.5^3}{2^9.3^8.5^3-2^{12}.3^8.5^3}=\frac{2^8.3^8.5^3\left(2^2.3+1\right)}{2^9.3^8.5^3\left(1-2^3\right)}\)
\(=\frac{13}{2.-7}=-\frac{13}{14}\)