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Bài 5 :
\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{59}\)
\(A=1-\frac{1}{50}\)
từ trên ta có : \(1-\frac{1}{50}< 1\)
\(\Rightarrow A< 1\)
\(A=\frac{72^3.54^2}{108^4}=\frac{\left(2^3.3^2\right)^3.\left(2.3^3\right)^2}{\left(2^2.3^3\right)^4}=\frac{2^9.3^6.2^2.3^6}{2^8.3^{12}}=\frac{2^{11}.3^{12}}{2^8.3^{12}}=\frac{2^3}{1}=8\)
\(=\frac{9^3.8^3.9^2.6^2}{9^4.3^4.4^4}=\frac{9^5.4^3.2^3.2^2.3^2}{9^4.4^4.3^4}\)\(=\frac{9.2^3.2^2}{4.3^2}=2^3=8\)
\(=\frac{9^3.8^3.9^2.6^2}{9^4.12^4}=\frac{9.4^3.2^3.3^2.2^2}{3^4.4^4}=\frac{9.2^3.2^2}{3^2.4}\) =23=8
\(=\frac{\left(2^3.3^2\right)^3.\left(2.3^3\right)^2}{\left(2^2.3^3\right)^4}=\frac{2^9.3^6.2^2.3^6}{2^8.3^{12}}=\frac{2^{9+2}.3^{6+6}}{2^8.3^{12}}=\frac{2^{11}.3^{12}}{2^8.3^{12}}=2^3=8\)
A = \(\dfrac{72^3.5^{42}}{108^4}\)
= \(\dfrac{\left(2^3.3^2\right)^3.5^{42}}{\left(2^2.3^3\right)^4}\)
= \(\dfrac{2^9.3^6.5^{42}}{2^8.3^{12}}\)
= \(\dfrac{2.5^{42}}{3^6}\)
@trần phúc nguyên
B = \(\dfrac{45^3.20^4.18^2}{180^5}\)
= \(\dfrac{\left(3^2.5\right)^3\left(2^2.5\right)^4.\left(2.3^2\right)^2}{\left(2^2.3^2.5\right)^5}\)
= \(\dfrac{3^6.5^3.2^8.5^4.2^2.3^4}{2^{10}.3^{10}.5^5}\)
= \(\dfrac{3^{10}.5^7.2^{10}}{2^{10}.3^{10}.5^5}\)
= 25
@trần phúc nguyên
\(A=\frac{72^3.54^2}{108^4=}=\frac{2^9.3^6.2^2.3^6}{2^8.3^{12}}=2^3=8\)