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Ta có: \(A=\frac{3}{1\cdot5}+\frac{3}{5\cdot4}+\frac{3}{4\cdot11}+...+\frac{3}{73\cdot149}+\frac{3}{149\cdot76}\)
\(\Rightarrow A=\frac{1}{2}\cdot\left(\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+...+\frac{3}{146\cdot149}+\frac{3}{149\cdot152}\right)\)
\(\Rightarrow A=\frac{1}{2}\cdot\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{146}-\frac{1}{149}+\frac{1}{149}-\frac{1}{152}\right)\)
\(\Rightarrow A=\frac{1}{2}\cdot\left(\frac{1}{2}-\frac{1}{152}\right)=\frac{1}{2}\cdot\left(\frac{76}{152}-\frac{1}{152}\right)=\frac{1}{2}\cdot\frac{75}{152}=\frac{75}{304}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) ( 137 - 529 ) + ( 137 + 529 )
= 137 - 529 + 137 + 529
= ( -529 + 529 ) + (137 + 137 )
= 0 + 274
= 274
b) ( 125 - 571 = 145 ) - ( 125 - 571 )
bạn ghi sai dấu nên mình sửa lại nha
b) ( 125 - 571 + 145 ) - ( 125 - 571 )
= 125 - 571 + 145 - 125 + 571
= ( 125 -125 ) + ( -571 + 571 ) +145
= 0 + 0 + 145
=145
![](https://rs.olm.vn/images/avt/0.png?1311)
a
=> \(x+2=\dfrac{484}{44}=11\)
=> x = 11 - 2 = 9
b
=> \(x+321=34.12=408\)
=> x = 408 - 321 = 87
c
=> \(x-210=246.15=3690\)
=> x = 3690 + 210 = 3900
d
=> \(205-x=\dfrac{420}{84}=5\)
=> x = 205 - 5 = 200
a: =>x+2=11
=>x=9
b: =>x+321=408
=>x=87
c: =>x-210=3690
=>x=3900
d: =>205-x=5
=>x=200
=-1771956
d: =5073-489-73+489-100
=5000-100
=4900