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Ta có 5/2 + 5/4 + 5/8 + 5/16 + 5/32 + 5/64 + 5/128 + 5/256
= 5- 5/2 + 5/2 - 5/4 + 5/4 - 5/8 + 5/8 - 5/16 + 5/16 - 5/32 + 5/32 - 5/64 + 5/64 - 5/128 + 5/128 - 5/256
= 5-5/256
= 1275/256
b ) Đặt \(A=\frac{5}{1.3}+\frac{5}{3.5}+\frac{5}{5.7}+...+\frac{5}{101.103}\)
\(\Rightarrow A=\frac{5}{2}\left(\frac{5}{1}-\frac{5}{3}+\frac{5}{3}-\frac{5}{5}+....+\frac{5}{101}-\frac{5}{103}\right)\)
\(\Rightarrow A=\frac{5}{2}\left(5-\frac{5}{103}\right)\)
= (3/5 + 2/5) + (3/4 + 1/2)
= 1 + 5/4
= 9/4
ko biết có cần đổi ra số thập phân hay ko?
\(\frac{1}{6}:\frac{4}{5}+\frac{1}{8}:\frac{4}{5}=\left(\frac{1}{6}+\frac{1}{8}\right):\frac{4}{5}=\left(\frac{4}{24}+\frac{3}{24}\right).\frac{5}{4}=\frac{7}{24}.\frac{5}{4}=\frac{35}{96}\)
\(\frac{1}{6}:\frac{4}{5}-\frac{1}{8}:\frac{4}{5}=\left(\frac{1}{6}-\frac{1}{8}\right):\frac{4}{5}=\left(\frac{4}{24}-\frac{3}{24}\right).\frac{5}{4}=\frac{1}{24}.\frac{5}{4}=\frac{5}{96}\)
a) 1/6 : 4/5 + 1/8 : 4/5 b) 1/6 : 4/5 - 1/8 : 4/5
= 4/5 : ( 1/6 + 1/8 ) = 4/5 : ( 1/6 - 1/8 )
= 4/5 : 7/24 = 4/5 : 1/24
= 96/35 = 96/5
=(3/5+2/5)+(3/4+5/8+1/2)
=1+15/8
=23/8
=4(25+32+39+46+53)
=4.195
=780
Nhớ vote cho mình nha
3/5+3/4+2/5+5/8+1/2=(3/5+2/5)+(6/8+5/8+4/8)=1+15/8=23/8
4.25+4.32+4.39+4.46+4.53=4.(25+32+39+46+53)=4.195=780
\(\frac{5}{2}+\frac{5}{4}+\frac{5}{8}+\frac{5}{16}+\frac{5}{32}+\frac{5}{64}+\frac{5}{128}+\frac{5}{256}\)
\(\Rightarrow5-\frac{5}{2}+\frac{5}{2}-\frac{5}{4}+\frac{5}{4}-\frac{5}{8}+\frac{5}{8}-\frac{5}{16}+...+\frac{5}{128}-\frac{5}{256}\)
\(\Rightarrow5-\frac{5}{256}\)
\(\Rightarrow\frac{1275}{256}\)
KQ 1275/256