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a) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}+\frac{55}{56}+\frac{71}{72}+\frac{89}{90}\)
\(=1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+1-\frac{1}{30}+1-\frac{1}{42}+1-\frac{1}{56}+1-\frac{1}{72}+1-\frac{1}{90}\)
\(=8-\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)
\(=8-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(=8-\left(\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}+\frac{6-5}{5.6}+\frac{7-6}{6.7}+\frac{8-7}{7.8}+\frac{9-8}{8.9}+\frac{10-9}{9.10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)=7,6\)
b) Bạn làm tương tự.
\(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
\(=1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)
\(=8-\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)
\(=8-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)\)
\(=\frac{38}{5}\)
Sửa đề: \(2x+\dfrac{11}{6}+\dfrac{23}{12}+\dfrac{39}{20}+\dfrac{59}{30}+\dfrac{83}{42}+\dfrac{111}{56}=12\)
\(\Leftrightarrow2x+\left(2+2+2+2+2+2\right)-\left(\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\right)=12\)
\(\Leftrightarrow2x-\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{7}-\dfrac{1}{8}\right)=0\)
\(\Leftrightarrow2x-\dfrac{3}{8}=0\)
hay x=3/16
`A)15/9=(5 xx 3)/(3 xx 3)=5/3`
`60/(-96)=(5 xx 12)/(12 xx (-8))=-5/8`
`=>5/3=15/9`
Ta thấy trừ cặp `5/3=15/9` thì còn lại không bằng nhau.
`B)60/(-85)=(5 xx 12)/(5 xx (-17))=-12/17`
`-77/56=(7 xx (-11))/(8 xx 7)=-11/8`
`=>-12/17=60/(-85)`
Ta thấy trừ cặp `-12/17=60/(-85)` thì còn lại không bằng nhau.
a) \(\dfrac{15}{9}=\dfrac{5}{3}\)
b) \(-\dfrac{12}{17}=\dfrac{60}{-85}\)
A = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
A = 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8
A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8
A = 1 + ( -1/2 + 1/2 ) + ( -1/3 + 1/3 ) + ( -1/4 + 1/4 ) + ( -1/5 + 1/5 ) + ( -1/6 + 1/6 ) + ( -1/7 + 1/7 ) - 1/8
A = 1 + 0 + 0 + 0 + 0 + 0 + 0 - 1/8
A = 1 - 1/8
A = 7/8
* Sửa đề tí nhé
B = 3/2 - 5/6 + 7/12 - 9/20 + 11/30 - 13/42 + 15/56
B = 3/1.2 - 5/2.3 + 7/3.4 - 9/4.5 + 11/5.6 - 13/6.7 + 15/7.8
B = 3 - 3/2 - 5/2 - ( -5/3 ) + 7/3 - 7/4 - 9/4 - ( -9/5 ) + 11/5 - 11/6 - 13/6 - ( -13/7 ) + 15/7 - 15/8
B = 3 - 3/2 - 5/2 + 5/3 + 7/3 - 7/4 - 9/4 + 9/5 + 11/5 - 11/6 - 13/6 + 13/7 + 15/7 - 15/8
B = 3 + ( -3/2 - 5/2 ) + ( 5/3 + 7/3 ) + ( -7/4 - 9/4 ) + ( 9/5 + 11/5 ) + ( -11/6 - 13/6 ) + ( 13/7 + 15/7 ) - 15/8
B = 3 + -4 + 4 + -4 + 4 + -4 + 4 - 15/8
B = 3 + 0 + 0 + 0 - 15/8
B = 3 - 15/8
B = 9/8
B) (-11)+350+16+(-350 )
= - 11 + 350 + 16 - 350 )
= ( - 11 + 16 ) + ( 350 - 350 )
= 5 + 0 =5
C) (-10)+23+(-20)+30
= - 10 + 23 - 20 + 30
= ( - 10 - 20 + 30 ) + 23
= - 30 + 30 + 23
= 0 + 23 = 23
D) (456-123)+123
= 456 - 123 + 123
= 456
E) (-102)-(345-102)
= - 102 - 345 + 102
= ( - 102 + 102 ) - 345
= 0 - 345
= - 345
F) (12-34)-(34-8)
= 12 - 34 - 34 - 8
= (12 - 8 ) + ( -34 - 34 )
= 4 - 68
= 64
G) (12+34-56)-(12-56)
= 12 + 34 - 56 - 12 +56
= ( 12 - 12 ) + ( -56 + 56 ) + 34
= 0 + 0 + 34
= 34
Câu F k giống tính nhanh ____ Có thể là bạn gõ sai đề
@@ Học tốt @@
## Chiyuki Fujito
b ) (-11) + 350 + 16 + (-350)
= (16 - 11 ) + ( 350 - 350 )
= 5 + 0
= 5
c) (-10) + 23 + (-20) + 30
= 23 + ( 30 - 10 - 20 )
= 23 + 0
= 23
d) ( 456 - 123 ) + 123
= 456 - ( 123 - 123 )
= 456 - 0
= 456
e) ( - 102 ) - ( 345 - 102 )
= - 345 - ( 102 - 102 )
= - 345 - 0
= - 345
\(=1-\dfrac{1}{2}+1-\dfrac{1}{6}+1-\dfrac{1}{12}+1-\dfrac{1}{20}+1-\dfrac{1}{30}+1-\dfrac{1}{42}+1-\dfrac{1}{56}\)
\(=7-\left(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{56}\right)\)
\(=7-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{7}-\dfrac{1}{8}\right)\)
\(=7-\dfrac{7}{8}=\dfrac{49}{8}\)
a)11+11+11+11+11+11+11+11+11=\(11^9\)=99.
b)56+56+12+12+12+20+56+56+56=56+56+56+56+56+56=\(56^6\)=336.
c)\(45^8\)=360.
d)\(12^4\)=48
a)11+11+11+11+11+11+11+11+11=\(11^9\)=99.
b)56+56+12+12+12+20+56+56+56=56+56+56+56+56+56=\(56^6\)=336.
c)\(45^8\)=360.
d)\(12^4\)=48