\(I=\dfrac{3}{8^3}+\dfrac{3}{8^4}=\dfrac{3.8}{8^4}+\dfrac{3}{8^4}=\dfrac{27}{8^4}\)
\(K=\dfrac{7}{8^3}+\dfrac{7}{8^4}=\dfrac{7.8}{8^4}+\dfrac{7}{8^4}=\dfrac{63}{8^4}\)
Vậy \(I< K\) vì \(\dfrac{27}{8^4}< \dfrac{63}{8^4}\)
Tính hợp lí:
g) \(\dfrac{-3}{4}+\dfrac{2}{7}+\dfrac{-1}{4}+\dfrac{3}{5}+\dfrac{5}{7}\)
h) \(\dfrac{7}{19}.\dfrac{8}{11}+\dfrac{7}{19}.\dfrac{3}{11}-\dfrac{12}{19}\)
i) \(19\dfrac{5}{8}:\dfrac{7}{2013}-26\dfrac{5}{8}:\dfrac{7}{2013}\)
k) \(\dfrac{-5}{12}.\dfrac{2}{11}+\dfrac{-5}{12}.\dfrac{9}{11}+\dfrac{5}{12}\)
Cho A = 40 + \(\dfrac{3}{8}+\dfrac{7}{8^2}+\dfrac{5}{8^3}+\dfrac{32}{8^5}\)
B = \(\dfrac{24}{8^2}+40+\dfrac{5}{8^2}+\dfrac{40}{8^4}+\dfrac{5}{8^4}\)
So sánh A và B
\(\dfrac{-1}{8}+\dfrac{-5}{8}\)
\(\dfrac{-3}{7}+\dfrac{5}{7}\)
\(\dfrac{3}{5}+\dfrac{-7}{4}\)
\(\dfrac{-2}{3}+\dfrac{1}{5}\)
\(\dfrac{-2}{13}+\dfrac{-5}{26}\)
\(\dfrac{-4}{7}+\dfrac{1}{3}\)
B5: Tính hợp lý:
a, \(\dfrac{11}{22}-\dfrac{3}{16}.\dfrac{8}{18}+\dfrac{1}{18}\)
b, \(\dfrac{5}{7}+\dfrac{3}{7}:4-\dfrac{8}{9}.\dfrac{-3}{4}\)
d) \(\dfrac{-3 }{7 } + \dfrac{5 }{ 13 }+ \dfrac{-4 }{ 7}\)
\(e ) \dfrac{-5}{21}+ \dfrac{-2}{21}+\dfrac{-8}{24}\) \(\dfrac{-3 }{7 } + \dfrac{5 }{ 13 }+ \dfrac{-4 }{ 7}\)\( e)\dfrac{-5 }{ 21} + \dfrac{-2 }{21 } + \dfrac{-8 }{ 4}\)
f
4, so sánh A và B:
a,A=\(\dfrac{3}{8^3}+\dfrac{7}{8^4}\);B=\(\dfrac{7}{8^3}+\dfrac{3}{8^4}\)
b,A=\(\dfrac{10^7+5}{10^7-8}\);B=\(\dfrac{10^8+6}{10^8-7}\)
c,A=\(\dfrac{10^{1992}+1}{10^{1991}+1}\);B=\(\dfrac{10^{1993}+1}{10^{1992}+1}\)
Tính bằng cách hợp lý:
\(a,\dfrac{2}{3}+\left(\dfrac{5}{7}+\dfrac{-2}{3}\right)\)
\(b,\left(\dfrac{-1}{4}+\dfrac{5}{8}\right)+\dfrac{-3}{8}\)
\(c,\dfrac{7}{5}.\dfrac{8}{19}+\dfrac{7}{5}.\dfrac{12}{19}-\dfrac{7}{5}.\dfrac{1}{19}\)
\(d,6\dfrac{3}{10}-\left(3\dfrac{4}{7}+2\dfrac{3}{10}\right)\)
\(e,\left(31,12-5,97\right)-\left(-68,88+4,03\right)\)
\(h,3,7.\left(-10,56\right)+3,7.110,56\)
cặp phân số nào bằng nhau :
\(A\) \(\dfrac{-3}{4}\)và \(\dfrac{-4}{3}\)
B \(\dfrac{-2}{3}\)và\(\dfrac{6}{9}\)
C 3/7 và \(\dfrac{-3}{7}\)
D 7/8 và \(\dfrac{-35}{-40}\)
Bài 4: So sánh:
a. \(\dfrac{2}{3}\)và\(\dfrac{1}{4}\)
b. \(\dfrac{7}{10}\)và\(\dfrac{7}{8}\)
c. \(\dfrac{6}{7}\)và\(\dfrac{3}{5}\)
d. \(\dfrac{14}{21}\)và\(\dfrac{60}{72}\)
