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\(=\dfrac{5^{15}\left(18+7\right)}{5^{17}}=\dfrac{5^{17}}{5^{17}}=1\)

Bài 1:
a; \(\dfrac{5}{18}\) + \(\dfrac{8}{19}\) - \(\dfrac{7}{21}\) + (- \(\dfrac{10}{36}\) + \(\dfrac{11}{19}\) + \(\dfrac{1}{3}\)) - \(\dfrac{5}{8}\)
= \(\dfrac{5}{18}\) + \(\dfrac{8}{19}\) - \(\dfrac{1}{3}\) -\(\dfrac{10}{36}\) + \(\dfrac{11}{19}\) + \(\dfrac{1}{3}\) - \(\dfrac{5}{8}\)
= (\(\dfrac{5}{18}\) - \(\dfrac{10}{36}\)) + (\(\dfrac{8}{19}\) + \(\dfrac{11}{19}\)) - (\(\dfrac{1}{3}\) - \(\dfrac{1}{3}\)) - \(\dfrac{5}{8}\)
= (\(\dfrac{5}{18}\) - \(\dfrac{5}{18}\)) + \(\dfrac{19}{19}\) - 0 - \(\dfrac{5}{8}\)
= 0 + 1 - \(\dfrac{5}{8}\)
= \(\dfrac{3}{8}\)
b; \(\dfrac{1}{13}\) + (\(\dfrac{-5}{18}\) - \(\dfrac{1}{13}\) + \(\dfrac{12}{17}\)) - (\(\dfrac{12}{17}\) - \(\dfrac{5}{18}\) + \(\dfrac{7}{5}\))
= \(\dfrac{1}{13}\) - \(\dfrac{5}{18}\) - \(\dfrac{1}{13}\) + \(\dfrac{12}{17}\) - \(\dfrac{12}{17}\) + \(\dfrac{5}{18}\) - \(\dfrac{7}{5}\)
= (\(\dfrac{1}{13}\) - \(\dfrac{1}{13}\)) + (\(\dfrac{12}{17}\) - \(\dfrac{12}{17}\)) + (-\(\dfrac{5}{18}\) + \(\dfrac{5}{18}\)) - \(\dfrac{7}{5}\)
= 0 + 0 + 0 - \(\dfrac{7}{5}\)
= - \(\dfrac{7}{5}\)
Bài 1 c;
\(\dfrac{15}{14}\) - (\(\dfrac{17}{23}\) - \(\dfrac{80}{87}\) + \(\dfrac{5}{4}\)) + (\(\dfrac{17}{23}\) - \(\dfrac{15}{14}\) + \(\dfrac{1}{4}\))
= \(\dfrac{15}{14}\) - \(\dfrac{17}{23}\) + \(\dfrac{80}{87}\) - \(\dfrac{5}{4}\) + \(\dfrac{17}{23}\) - \(\dfrac{15}{14}\) + \(\dfrac{1}{4}\)
= (\(\dfrac{15}{14}-\dfrac{15}{14}\)) + (\(-\dfrac{17}{23}+\dfrac{17}{23}\)) - (\(\dfrac{5}{4}\) - \(\dfrac{1}{4}\)) + \(\dfrac{80}{87}\)
= 0 + 0 - 1 + \(\dfrac{80}{87}\)
= - \(\dfrac{7}{87}\)

\(\frac{5^{15}.18+5^{15}.7}{5^{17}}\)
\(=\frac{5^{15}.\left(18+7\right)}{5^{17}}\)
\(=\frac{5^{15}.25}{5^{17}}\)
\(=\frac{5^{15}.5^2}{5^{17}}\)
\(=\frac{5^{17}}{5^{17}}\)
\(=1\)
(515.18 + 515.7) : 517
=\([5^{15}.(18+7)]:5^{17}\)
=515.25 : 517
=517:517
=1


a,-5/9 + 8/18 + -2/11 + 4/-9 + 7/15 b,5/17 + -9/15 + -2/17 + 2/5 + 14/17
= -5/9 + 4/9 + -2/+ 4/-9 + 7/15 = 5/17 + -3/5 + -2/17 + 2/5 + 14/17
=(-5/9 + 4/9 + -4/9 ) +-2/11 + 7/15 = ( 5/17 + -2/17 + 14/17) + ( 2/5 + -3/5)
= -1/3 + -2/11 + 7/15 =1 + -1/5
=-75/225 + -30/ 225 + 77/225 =4/5
= -25/225 = -1/9 ( 4/5 = 0.8 )


a, 75 - 5 . ( 15 - 10 ) - ( -60 ) = 75 - 5 . 5 + 60 = 135 - 25 = 110
b, 136 - ( -7 ) + 6 - 23 - 36 = 136 + 7 + 6 - 23 - 36 = ( 136 - 36 ) + ( 7 + 6 - 23 ) = 100 - 10 = 90
c, ( -15 - 17 ) . ( -15 + 7 ) = -32 . ( -8 ) = 256
d, ( -9 - 18 ) : ( -9 ) = -27 : ( -9 ) = 3
Bài 2:
a, 2x - 17 = ( -3x - 18 )
<=> 2x + 3x = 17 - 18
<=> 5x = -1
<=> x = -1/5
b, ( 13 - IxI ) + 15 = 20
<=> 13 - |x| = 5
<=> |x| = 8
<=> x = 8 hoặc x = -8
c, Ix + 5I - ( x + 5 ) = 0
<=> |x + 5| = x + 5
Đk: x + 5 ≥ 0 => x ≥ -5
\(\Leftrightarrow\orbr{\begin{cases}x+5=x+5\\x+5=-x-5\end{cases}\Leftrightarrow}\orbr{\begin{cases}0x=0\\2x=-10\end{cases}\Leftrightarrow}\orbr{\begin{cases}x\ge-5\\x=-5\end{cases}}\)
Vậy x ≥ -5

a, 45 -5 .( 17 +9 ) - 17.(-15)
= 45 - 5 .17 - 5 .9 - 17 .(-15)
= (45 - 5.9 )- 5 .17 + 17 .15
= 0 + 17 .( -5 +15)
= 17 .10
=170
b, 45 . (18 - 15 ) -18.(45+5 )
= 45 .18 - 45 . 15 - 18 . 45 -18.5
= 45.18 - 18.5 - 45.15 -18.45
= 45.18-18.45 -6.15-45.15
= 0 + 15. (-6-45 )
= 15. (-51)
= -39015

1, ( x - 12 ) -15 = ( 20 - 7 ) - ( 18 +x )
( x- 1 2) - 15 = 3 - (18 +x)
( x - 12) + (18 + x) = 3 + 15
x - 12 + 18 +x = 18
2x + 6 = 18
2x = 18 - 6
2x = 12
x = 12 : 2
x = 6
2; ( 3x- 17 ) + 2 ( 5- 2x) + 5x = 19
3x - 17 + 10 - 4x + 5x = 19
4x - 7 = 19
4x = 19 + 7
4x = 26
x = 26 : 4
x = 13/2
a,(x-12)-15=(20-7)-(18+x)
x-12-15=3-18-x
x-27=-15-x
x+x=27-15
2x=12
x=6
b,(3x-17)+2(5-2x)+5x=19
3x-17+10-4x+5x=19
3x-4x+5x=19+17-10
4x=26
x=6.5