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đề bài \(\frac{5\cdot4^{15}\cdot\left(-9\right)^9-4\cdot3^{20}\cdot8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\)
Giải:
\(\frac{5\cdot4^{15}\cdot\left(-9\right)^9-4\cdot3^{20}\cdot8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\)=\(\frac{5.\left(2^2\right)^{15}.\left(-3^2\right)^9-2^2.3^{20}.\left(2^3\right)^9}{5.2^9.\left(2.3\right)^{19}-7.2^{29}.\left(3^3\right)^6}=\frac{-5.2^{30}.3^{18}-2^2.3^{20}.2^{27}}{5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}}\)
=\(\frac{-5.2^{30}.3^{18}-2^{29}.3^{20}}{5.2^{28}.3^{19}-7.2^{29}.3^{18}}\)
=\(\frac{-2^{29}.3^{18}.\left(5.2+3^2\right)}{2^{28}.3^{18}.\left(5.3-7.2\right)}\)
=\(\frac{-2^{29}.3^{18}.19}{2^{28}.3^{18}.1}\)
=\(=-2.19=-38\)
\(=\dfrac{5\cdot2^{30}\cdot3^{18}-2^{29}\cdot3^{20}}{5\cdot2^{29}\cdot3^{19}-7\cdot2^{29}\cdot3^{18}}=\dfrac{2^{29}\cdot3^{18}\left(5\cdot2-3^2\right)}{2^{29}\cdot3^{18}\left(5\cdot3-7\right)}=\dfrac{10-9}{15-7}=\dfrac{1}{8}\)
\(\dfrac{5.4^{15}.9^9-4.3^{20}.8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\) (sửa \(-9^9\rightarrow.9^9\))
\(=\dfrac{5.2^{30}.3^{18}-2^2.3^{20}.2^{27}}{5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}}\)
\(=\dfrac{5.2^{30}.3^{18}-2^{29}.3^{20}}{5.2^{28}.3^{19}-7.2^{29}.3^{18}}\)
\(=\dfrac{2^{29}.3^{18}\left(15-9\right)}{2^{28}.3^{18}\left(15-14\right)}\)
\(=2.6=12\)
=\(\frac{5\cdot2^{30}\cdot3^{18}-2^2\cdot3^{20}\cdot2^{27}}{5\cdot2^9\cdot\left(2\cdot3\right)^{19}-7\cdot2^{29}\cdot3^{18}}\)=\(\frac{5\cdot2^{30}\cdot3^{18}-3^{20}\cdot2^{29}}{5\cdot2^{28}\cdot3^{19}-7\cdot2^{29}\cdot3^{18}}\)=\(\frac{2^{29}\cdot3^{18}\cdot\left(5\cdot2-3^2\right)}{2^{28}\cdot3^{18}\left(5\cdot3-7\cdot2\right)}\)=2
^ là 6 đúng không
-_- bó tay