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a, ( 1/2 - 13/14 ) : 5/7 - ( -2/21 + 1/7 ) : 5/7
= ( 7/14 - 13/14 ) : 5/7 - ( -2/21 + 3/21 ) : 5/7
= -3/7 : 5/7 - 1/21 : 5/7
= -3/7 . 7/5 - 1/21 . 7/5
= ( -3/7 - 1/21 ) . 7/5
= ( -9/7+ -1/21 ) . 7/5
= -10/21 . 7/5
= -2/3
b, (68/5 + 19/4 ) - 43/5
= 68/5 + 19/4 - 43/5
= ( 68/5 - 43/5 ) + 19/4
= 5 +19/4
= 39/4
c, ( 93/11 + 29/8 ) - 38/11
= 93/11 + 29/8 - 38/11
= ( 93/11 - 38/11 ) + 29/8
= 5 + 29/8
=69/8
d, 4/9 : ( -1/7 ) + 59/9 : ( -1/7 )
= 4/9 . -7 + 59/9 . -7
= ( 4/9 + 59/9 ) . -7
= 7 . -7
= -49

a: \(=\dfrac{7}{2}\left(-\dfrac{3}{4}+\dfrac{5}{13}-\dfrac{9}{4}-\dfrac{8}{13}\right)=\dfrac{7}{2}\cdot\left(-3-\dfrac{3}{13}\right)=\dfrac{7}{2}\cdot\dfrac{-42}{13}=\dfrac{-147}{13}\)
b: \(=-12+\dfrac{8}{9}-\dfrac{5}{18}=\dfrac{-216}{18}+\dfrac{16}{18}-\dfrac{5}{18}=\dfrac{-205}{18}\)
c: \(=\dfrac{45}{4}-\dfrac{19}{7}-\dfrac{21}{4}=6-\dfrac{19}{7}=\dfrac{23}{7}\)
d: \(=\dfrac{-1}{4}\left(\dfrac{152}{11}+\dfrac{68}{11}\right)=\dfrac{-1}{4}\cdot20=-5\)

Bài 2:
a) \(\frac{2}{3}\) - 4 .(\(\frac{1}{2}\) + \(\frac{3}{4}\)) = \(\frac{2}{3}\) - 4 . \(\frac{5}{4}\)
= \(\frac{2}{3}\) - 5 = \(\frac{-13}{3}\)
b) (\(\frac{-1}{3}\) + \(\frac{5}{6}\)) . 11 - 7 = \(\frac{1}{2}\). 11 - 7
= \(\frac{11}{2}\)- 7 = \(\frac{-3}{2}\)
c) \(\frac{-5}{9}\). \(\frac{3}{11}\)+ (\(\frac{-13}{18}\)) . \(\frac{3}{11}\)= \(\frac{3}{11}\). (\(\frac{-5}{9}\)- \(\frac{13}{18}\))
= \(\frac{3}{11}\). (\(\frac{-23}{18}\))= \(\frac{-23}{66}\)
d) \(\frac{-2}{3}\) . \(\frac{3}{11}\)+ (\(\frac{-16}{9}\)) . \(\frac{3}{11}\)= \(\frac{3}{11}\). (\(\frac{-2}{3}\)- \(\frac{16}{9}\))
= \(\frac{3}{11}\). (\(\frac{-22}{9}\)) = \(\frac{-2}{3}\)
Bài 1:
a) =\(\frac{-1}{2}\)+ \(\frac{3}{5}\)- \(\frac{1}{9}\)+ \(\frac{1}{71}\) + \(\frac{2}{7}\) + \(\frac{4}{35}\)- \(\frac{7}{18}\)
= (\(\frac{-1}{2}\)- \(\frac{1}{9}\)- \(\frac{7}{18}\)) + ( \(\frac{3}{5}\)+ \(\frac{2}{7}\)+ \(\frac{4}{35}\)) + \(\frac{1}{71}\)
= -1 + 1 + \(\frac{1}{71}\)= \(\frac{1}{71}\)
b) = 3 - \(\frac{1}{4}\)+ \(\frac{2}{3}\)- 5 + \(\frac{1}{3}\)+ \(\frac{6}{5}\)- 6 + \(\frac{7}{4}\)- \(\frac{3}{2}\)
= (3 - 5 - 6) + (\(\frac{-1}{4}\)+ \(\frac{7}{4}\)- \(\frac{3}{2}\)) + (\(\frac{2}{3}\)+ \(\frac{1}{3}\)) + \(\frac{6}{5}\)
= -8 + 0 + 1 + \(\frac{6}{5}\)
= \(\frac{-29}{5}\)

a, 7/12 - 3/4 . 5/6
= 7/12 - 5/8
= 14/24- 15/24
= -1/24
b,( 2/1/3 + 1/3/4 ) . 12/13
= ( 6/3 + 7/3 ) . 12/13
= 13/3 . 12/13
=4
c, 12 : ( 3/4 -5/6 ) . 2
= 12 : ( -1/12 ) .2
= 12 . -12 . 2
= -228
d, 7/22 : 3/11 + 7/22 : 4/11
= 7/22 . 11/3 + 7/22 . 11/4
= 7/22 . ( 11/3 + 11/4 )
....
tiếp theo bạn tự làm nhé!

1)
a. \(\left(3x^2-50\right)^2=5^4\)
\(\Leftrightarrow3x^4-50=625\)
\(\Leftrightarrow3x^4=675\)
\(\Leftrightarrow x^4=225\)
\(\Leftrightarrow x=\sqrt{15}\)
2)
a. \(\frac{\left(3^4-3^3\right)^4}{27^3}=\frac{3^{16}-3^{12}}{\left(3^3\right)^3}=\frac{3^{12}.3^4-3^{12}}{3^9}=\frac{3^{12}\left(3^4-1\right)}{3^9}\)
\(=\frac{3^{12}.80}{3^9}=3^3.80=27.80=2160\)
b. \(\frac{25^3}{\left(5^5-5^3\right)^2}=\frac{\left(5^2\right)^3}{5^{10}-5^6}=\frac{5^6}{5^6.5^4-5^6}=\frac{5^6}{5^6\left(5^4-1\right)}\)
\(=\frac{5^6}{5^6.624}=\frac{1}{624}\)

1.
a)=1/3-[(-5/4)-5/8]
=1/3-(-15/8)=53/24
b)=5/9:(-3/22)+5/9:(-3/5)
=5/9*22/-3+5/9*5/-3=-110/27+-25/27=5
2
a)Ta có 339<340=920<1120<1121
nên 339<1121
b)Ta có /3,4-x/ lớn hơn hoặc bằng 0 Với mọi x thuộc R
=> -/3,4-x/ bé hơn hoặc bằng 0 Với mọi x thuộc R
=> 0,5-/3,4-x/ bé hơn hoặc bằng 0,5 Với mọi x thuộc R
Dấu = xảy ra khi 3,4-x=0
=>x=3,4
Vậy GTLN của A = 0,5 khi x=3,4