Ôn tập về phân số

\(1-\dfrac{2}{11}=\dfrac{11}{11}-\dfrac{2}{11}=\dfrac{9}{11}\)

A

A

A

9/16

9/16

9/16

a) 3/14 x 2= 3/14 x 2/1 = 6/14 = 3/7
b) 3 x 7/9= 3/1 x 7/9 = 7/3
c) 4/11 : 2= 4/11 : 2/1 = 4/11 x 1/2 = 4/22= 2/11
d) 4 x 5/8= 4/1 x 5/8 = 20/8 = 5/2

đăng mấy câu rồi ...?

spam:v

`a) 3 / 14 xx 2 = [ 3 xx 2 ] / [ 7 xx 2 ] = 3 / 7`

`b) 3 xx 7 / 9 = [ 3 xx 7 ] / [ 3 xx 3 ] = 7 / 3`

`c) 4 / 11 : 2 = 4 / 11 xx 1 / 2 = [ 2 xx 2 ] / [ 11 xx 2 ] = 2 / 11`

`d) 4 xx 5 / 8 = [ 4 xx 5 ] / [ 4 xx 2 ] = 5 / 2`

a) 3/14 x 2= 3/14 x 2/1 = 6/14 = 3/7
b) 3 x 7/9= 3/1 x 7/9 = 7/3
c) 4/11 : 2= 4/11 : 2/1 = 4/11 x 1/2 = 4/22= 2/11
d) 4 x 5/8= 4/1 x 5/8 = 20/8 = 5/2

=\(\dfrac{64}{192}+\dfrac{32}{192}+\dfrac{16}{192}+\dfrac{8}{192}+\dfrac{4}{192}+\dfrac{2}{192}+\dfrac{1}{192}\)

= \(\dfrac{127}{192}\)

Đặt \(S=\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{24}+\dfrac{1}{48}+\dfrac{1}{96}+\dfrac{1}{192}\)

\(\Rightarrow3S=1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}\)

\(\Rightarrow6S=2+1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\)

\(\Rightarrow6S-3S=2-\dfrac{1}{64}\)

\(\Rightarrow3S=\dfrac{127}{64}\)

\(\Rightarrow S=\dfrac{127}{192}\)

\(=\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{12}+...+\dfrac{1}{96}-\dfrac{1}{192}\\ =\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{192}\\ =\dfrac{127}{192}\)

ta có:

A=nhân tử của 2 vế với 6

/3+1/6+1/12+1/24+1/48+1/96-1/3-1/6+1/12-1/24-1/48-1/96-1/192

6xA-A=6-1/192