Tính bằng cách thuận tiện nhất
\(\dfrac{7}{12}+\dfrac{4}{9}+\dfrac{1}{3}+\dfrac{5}{12}+2\)
\(\dfrac{6}{5}nhan\dfrac{3}{8}nhan\dfrac{5}{8}nhan\dfrac{6}{5}-\dfrac{4}{5}\)
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60x [7/12+4/15]
60x153/180
=9180/180
b 1/2x2/3x3/4x4/5x5/6x6/7x7/8x8/9=40320/4032
a: =4/5+1/5+2/3+1/3=1+1=2
b: =17/12+7/12+29/7-8/7=3+2=5
c: =3/5+2/5+16/7-1/7-1/7
=1+2=3
d: =2/5+3/5+2/3+1/3+7/4+1/4
=1+1+2
=4
Bài 3
a,26/100+0,009+41/100+0,24
0,26+0,09+0,41+0,24
(0,26+0,24)+(0,09+0,41)
0,5+0,5
=1
b,9+1/4+6+2/7+7+3/5+8+2/3+2/5+1/3+5/7+3/4
(9+6+7+8)+(2/7+5/7)+(1/4+3/4)+(3/5+2/5)+(2/3+1/3)
30+1+1+1+1
=34
Bài 4,5 khó quá mik ko bít lamf^^))
Bài 4: a, \(\dfrac{2008}{2009}\) < 1; \(\dfrac{10}{9}\) > 1
\(\dfrac{2008}{2009}\) < \(\dfrac{10}{9}\)
b, \(\dfrac{1}{a+1}\) và \(\dfrac{1}{a-1}\)
Ta có: a + 1 > a - 1 ⇒ \(\dfrac{1}{a+1}\) < \(\dfrac{1}{a-1}\)
a, \(=\dfrac{1+4}{5}+\dfrac{5+1+3}{9}=1+1=2\)
b, \(=\dfrac{1+4+2}{3}+\dfrac{1+2+5}{6}=\dfrac{6}{3}+\dfrac{8}{6}=2+\dfrac{4}{3}=\dfrac{6+4}{3}=\dfrac{10}{3}\)
a/\(-\dfrac{1}{6}+\left(-\dfrac{5}{8}+\dfrac{7}{6}\right)\)
\(=\left(-\dfrac{1}{6}+\dfrac{7}{6}\right)-\dfrac{5}{8}\)
\(=1-\dfrac{5}{8}\)
\(=\dfrac{8}{8}-\dfrac{5}{8}=\dfrac{3}{8}\)
b/\(\left(\dfrac{2}{5}\right)^2+5\dfrac{1}{2}\cdot\left(4,5-2\right)+\dfrac{2^3}{\left(-4\right)}\)
\(=\dfrac{4}{25}+\dfrac{11}{2}\cdot\dfrac{5}{2}+-\dfrac{2^3}{2^2}\)
\(=\dfrac{4}{25}+\dfrac{55}{4}+\left(-2\right)\)
\(=\dfrac{16}{100}+\dfrac{1375}{100}-\dfrac{200}{100}\)
\(=\dfrac{1191}{100}=11,91\)
\(\dfrac{7}{12}+\dfrac{4}{9}+\dfrac{1}{3}+\dfrac{5}{12}+2=\dfrac{7+5}{12}+\dfrac{4+3}{9}+2=1+\dfrac{7}{9}+2=3+\dfrac{7}{9}=\dfrac{34}{9}\)
\(\dfrac{6}{5}.\dfrac{3}{8}.\dfrac{5}{8}.\dfrac{6}{5}-\dfrac{4}{5}=\dfrac{6.3.5.6}{5.8.8.5}-\dfrac{4}{5}=\dfrac{27}{80}-\dfrac{4}{5}=-\dfrac{37}{80}\)