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\(\dfrac{4}{5}-\dfrac{3}{4}.\dfrac{4}{5}.\dfrac{3}{4}\)
\(=\dfrac{4}{5}-\dfrac{9}{20}\)
\(=\dfrac{16}{20}-\dfrac{9}{20}\)
\(=\dfrac{7}{20}\)
\(\frac{3^4.2^3-3^4.4}{3^5.3^2-3^5.5}=\frac{3^4.\left(2^3-4\right)}{3^5.\left(3^2-5\right)}=\frac{8-4}{3.\left(9-5\right)}=\frac{4}{3.4}=\frac{1}{3}\)
\(\frac{3^4\cdot2^3-3^4\cdot4}{3^5.3^2-3^5\cdot5}=\frac{3^4\left(8-4\right)}{3^5\left(9-5\right)}=\frac{4}{3\cdot4}=\frac{1}{3}\)
\(\dfrac{3}{4}.\dfrac{4}{5}.\dfrac{5}{6}.....\dfrac{99}{100 }\) Giải: \(=\dfrac{3}{1.4}.\dfrac{4}{1.5}.\dfrac{5}{1.6}...\dfrac{99}{1.100}\)
\(=\dfrac{4-1}{1.4}.\dfrac{5-1}{1.5}.\dfrac{6-1}{1.6}...\dfrac{100-1}{1.100}\)
\(=1-\dfrac{1}{4}.1-\dfrac{1}{5}.1-\dfrac{1}{6}...1-\dfrac{1}{100}\)
\(=1\left(\dfrac{1}{4}-\dfrac{1}{5}-\dfrac{1}{6}-...-\dfrac{1}{100}\right)\)
Bài làm:
\(A=\frac{3^4.2^3-3^4.4}{3^5.3^2-3^5.5}\)
\(A=\frac{2^2.3^4\left(2-1\right)}{3^5\left(3^2-5\right)}\)
\(A=\frac{4.1}{3.4}=\frac{1}{3}\)
\(4.4^3=4.64=256\)
nhanh giữ