Mình ghi kết quả thôi nhé!

a.2/3

b.1/3

c.3/2

d.18

e.21

f.6/5

g.53/60

h.-13/18

           giải

a) 1/3 +1/4 +1/12 = 2/3

b) 3/9 + 12/39 - 1/3  = 1/3

c) 72/36 - 1/2 = 3/2

d) 34 - 32 và 1/2 = 18

e) 68/2 - 52/4 = 21

g) 1/2 + 1/3 + 1/4 - 1/5 = 53/60

h) 32/72 - 21/18 = (-13/18)

Mình làm ngắn gọn nhanh nhất rồi đó, rút gon luôn rồi. nha

đề??

a) \(\dfrac{4}{5}-\left(\dfrac{1}{5}+\dfrac{1}{3}\right)=\dfrac{4}{5}-\left(\dfrac{3}{15}+\dfrac{5}{15}\right)=\dfrac{4}{5}-\dfrac{8}{15}=\dfrac{12}{15}-\dfrac{8}{15}=\dfrac{4}{15}\)

b) \(\dfrac{12}{7}-\left(\dfrac{3}{14}-1\right)=\dfrac{12}{7}-\left(-\dfrac{11}{14}\right)=\dfrac{12}{7}+\dfrac{11}{14}=\dfrac{5}{2}\)

c) \(\dfrac{11}{2}-9\cdot\left(\dfrac{7}{5}-\dfrac{1}{2}\right)=\dfrac{11}{2}-9\cdot\dfrac{9}{10}=\dfrac{11}{2}-\dfrac{81}{10}=\dfrac{55}{10}-\dfrac{81}{10}=-\dfrac{13}{5}\)

d) \(3\times9\left(\dfrac{4}{7}+\dfrac{3}{5}\right)=27\times\dfrac{41}{35}=\dfrac{1107}{35}\)

e) \(\left(\dfrac{1}{3}-\dfrac{1}{5}\right):2=\left(\dfrac{5}{15}-\dfrac{3}{15}\right):2=\dfrac{2}{15}:2=\dfrac{2}{15}\times\dfrac{1}{2}=\dfrac{1}{15}\)

f) \(\dfrac{123}{34}:\dfrac{1}{17}-\dfrac{21}{34}:\dfrac{1}{17}=\left(\dfrac{123}{34}-\dfrac{21}{34}\right):\dfrac{1}{17}=3:\dfrac{1}{17}=3\times17=51\)

\(A=\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+\dfrac{1}{3^4}+...+\dfrac{1}{3^{99}}\)

\(\Rightarrow\dfrac{A}{3}=\dfrac{1}{3^2}+\dfrac{1}{3^3}+\dfrac{1}{3^4}+...+\dfrac{1}{3^{100}}\)

\(\Rightarrow A-\dfrac{A}{3}=\dfrac{2A}{3}=\left(\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{99}}\right)-\left(\dfrac{1}{3^2}+\dfrac{1}{3^3}+\dfrac{1}{3^4}+...+\dfrac{1}{3^{100}}\right)\)

\(\Rightarrow\dfrac{2A}{3}=\left(\dfrac{1}{3^2}-\dfrac{1}{3^2}\right)+\left(\dfrac{1}{3^3}-\dfrac{1}{3^3}\right)+...+\left(\dfrac{1}{3^{99}}-\dfrac{1}{3^{99}}\right)+\left(\dfrac{1}{3}-\dfrac{1}{3^{100}}\right)=\dfrac{1}{3}-\dfrac{1}{3^{100}}\)

\(\Rightarrow2A=3\cdot\left(\dfrac{1}{3}-\dfrac{1}{3^{100}}\right)\)

\(\Rightarrow\text{A}=\dfrac{1-\dfrac{1}{3^{99}}}{2}\)

\(\Rightarrow A=\dfrac{1}{2}-\dfrac{1}{2.3^{99}}< \dfrac{1}{2}\)

Bài 1

23 x 11=253

35 x 11=385

93 x 11=1023

11 x 78=858

11 x 43=473

Bài 2

35 x 46=1610

78 x 26=2028

89 x 32=2848

56 x 32=1792