1/176; 1/336;1/546 ....tìm số thứ 20
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\(\frac{1}{6}\cdot\frac{1}{66}\cdot\frac{1}{176}\)
\(=\frac{1}{1\cdot6}+\frac{1}{6\cdot11}+\frac{1}{11\cdot16}\)
\(=\frac{1}{5}\left(\frac{5}{1\cdot6}+\frac{5}{6\cdot11}+\frac{5}{11\cdot16}\right)\)
\(=\frac{1}{5}\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}\right)\)
\(=\frac{1}{5}\left(1-\frac{1}{16}\right)\)
\(=\frac{1}{5}\cdot\frac{15}{16}\)
\(=\frac{3}{16}\)
=))
\(\frac{1}{6}+\frac{1}{66}+\frac{1}{176}\)
\(=\frac{1}{1\times6}+\frac{1}{6\times11}+\frac{1}{11\times16}\)
\(=\frac{1}{5}\times\left(\frac{5}{1\times6}+\frac{5}{6\times11}+\frac{5}{11\times16}\right)\)
\(=\frac{1}{5}\times\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}\right)\)
\(=\frac{1}{5}\times\left(1-\frac{1}{16}\right)\)
\(=\frac{1}{5}\times\frac{15}{16}\)
\(=\frac{3}{16}\)
C4 :
16 = 24 ; 80 = 24.5 ; 176 = 24.11
<-> ƯCLN(16, 80, 176) = 24 = 16.
Ta có:
\(16=2^4\)
\(80=2^4.5^4\)
\(176=2^4.11\)
\(ƯCLN(16;80;176)=2^4=16\)
\(#WendyDang\)
1/ ta có:
18=2.32
77=7.11
=>ƯCLN(18;77)=1
=>ƯC(18;77)=Ư(1)={1}
2/ ta có:
134=2.67
60=22.3.5
=>ƯCLN(134;60)=2
=>ƯC(134;60)=Ư(2)={1;2}
3/ ta có:
176=24.11
234=2.32.13
=>ƯCLN(176;234)=2
=>ƯC(176;234)=Ư(2)={1;2}
1/6+1/66+1/176+....+1/496.501
=1/1.6+1/6.11+1/11.16+....+1/496.501
=(1/5).(5/1.6+5/6.11+5/11.16+....+5/496.501)
=(1/5).(1-1/6+1/6-1/11+1/11-1/16+...+1/496-1/501)
=(1/5).(1-1/501)
=1/5 . 500/501
=100/501
Ta có: 1/6+1/66+1/176+1/336+...+1/496.501
=1/1.6+1/6.11+1/11.16+1/16.21+...+1/496.501
=1/5.(5/1.6+5/6.11+5/11.16+5/16.21+...+5/496.501)
=1/5.(1-1/6+1/6-1/11+1/11-1/16+1/16-1/21+...+1/496-1/501)
=1/5.(1-1/501)
=1/5.500/501
=100/501
a. 175 : 0,5 + 176 : 0,1 + 176 x 8 = chia cho 0,5 là nhân với 2 , chia cho 0,1 nhân với 10
= 176 x 2 + 176 x 10 + 176 x 8 = 176 x ( 2 + 8 + 10 ) = 176 x 20 = 3520
b. 102 + 3 x 51 + 204 + 51 = 102 = 51 x 2 ; 204 = 51 x 4 \(\Rightarrow\) 51 x 2 + 51 x 3 + 51 x 4 + 51
= 51 x ( 1 + 2 + 3 + 4 ) = 51 x 10 = 510