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CHI TIẾT!
Đề bài: Tính nhanh
Làm cách lớp 4 nha
\(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}+\dfrac{3}{128}+\dfrac{3}{512}\)
\(\dfrac{15}{8}+\dfrac{3}{32}+\dfrac{3}{128}+\dfrac{3}{512}\)
\(\dfrac{63}{32}+\dfrac{3}{128}+\dfrac{3}{512}\)
\(\dfrac{255}{128}+\dfrac{3}{512}\)
\(\dfrac{1023}{512}\)
\(=\dfrac{3}{2}+\dfrac{3}{2.4}+\dfrac{3}{4.8}+\dfrac{3}{8.16}+\dfrac{3}{16.32}\)
\(=\dfrac{3}{2}+\dfrac{3}{2}-\dfrac{3}{4}+\dfrac{3}{4}-\dfrac{3}{8}+\dfrac{3}{8}-\dfrac{3}{16}+\dfrac{3}{16}-\dfrac{3}{32}\)
\(=\dfrac{3}{2}-\dfrac{3}{32}=\dfrac{45}{32}\)
\(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}+\dfrac{3}{128}+\dfrac{3}{512}\)
\(\dfrac{15}{8}+\dfrac{3}{32}+\dfrac{3}{128}+\dfrac{3}{512}\)
\(\dfrac{63}{32}+\dfrac{3}{128}+\dfrac{3}{512}\)
\(\dfrac{255}{128}+\dfrac{3}{512}\)
\(\dfrac{1023}{512}\)
\(=\dfrac{3}{2}+\dfrac{3}{2.4}+\dfrac{3}{4.8}+\dfrac{3}{8.16}+\dfrac{3}{16.32}\)
\(=\dfrac{3}{2}+\dfrac{3}{2}-\dfrac{3}{4}+\dfrac{3}{4}-\dfrac{3}{8}+\dfrac{3}{8}-\dfrac{3}{16}+\dfrac{3}{16}-\dfrac{3}{32}\)
\(=\dfrac{3}{2}-\dfrac{3}{32}=\dfrac{45}{32}\)