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(X - 1005) x (1 + 3 + 5+ 7 + 9 + 11) = 1989 x 1990 x (70 - 35 x 2)
(X - 1005) x (11 + 1)[(11 - 1) : 2 + 1): 2] = 1989 x 1990 x 0
(X - 1005) x 36 = 0
X - 1005 = 0 : 36
X - 1005 = 0
X = 1005
( x - 1005 ) . ( 1 + 3 + 5 + 7 + 9 + 11 ) = 1989 . 1990 . ( 70 - 35 . 2 )
( x - 1005 ) . 36 = 1989 . 1990 . ( 70 - 70 )
( x - 1005 ) . 36 = 1989 . 1990 . 0
( x - 1005 ) . 36 = 0
x - 1005 = 0
x = 1005
y+y x 1/3 : 2/9 + y :2/7 = 252
y x 1 + y x (1/3 x 9/2 ) + y x 7/2 = 252
y x 1/1 + y x 3/2 + y x 7/2 = 252
y x (1/1 + 3/2 + 7/2 ) = 252
y x 6 = 252
y = 252 : 6
y = 42
<=>x.1+x.3/2+x.7/2=252
x.(1+3/2+7/2)=252
x.6=252
x=252:6
=>x=42
a)\(\frac{5}{9}\times x-1=\frac{8}{9}\)
\(\frac{5}{9}\times x=\frac{8}{9}+1\)
\(\frac{5}{9}\times x=\frac{17}{9}\)
\(x=\frac{17}{9}:\frac{5}{9}\)
\(x=\frac{17}{5}\)
(x + 9) + (x - 8) + (x + 7) + (x - 6) + (x + 5) + (x - 4) + (x + 3) + (x - 2) + (x -1) = 95.9
=> (x + 9) + (x - 8) + (x + 7) + (x - 6) + (x + 5) + (x - 4) + (x + 3) + (x - 2) + (x -1) = 855
=> x + 9 + x - 8 + x + 7 + x - 6 + x + 5 + x - 4 + x + 3 + x - 2 + x -1 = 855
=> ( x + x + x + x + x + x + x + x + x ) + ( 9 - 8 + 7 - 6 + 5 - 4 + 3 - 2 - 1 ) = 855
=> 9x + 3 = 855
=> 9x = 855 - 3
=> 9x = 852
=> x = 852 : 9
=> x = \(\frac{284}{3}\)
\(\text{K - 2016 = }\frac{\text{1 + ( 1 + 2 ) + ( 1 + 2 + 3 ) + ... + ( 1 + 2 + 3 + ... + 2017 )}}{\text{2017 x 1 + 2016 x 2 + 2015 x 3 + ... + 2 x 2016 + 1 x 2017}}\)
a = 1/2 - 1/3 + 2/5 : 1/2
= 1/6 + 4/5
= 29/30
b X x 3/10 + X x 1/4 + 89 = 100
X x ( 3/10 + 1/4 ) + 89 = 100
X x 11/20 + 89 = 100
X x 11/20 = 100 - 89
X x 11/20 = 11
X = 11 : 11/20
X = 20
x+x*\(\frac{1}{2}\):\(\frac{2}{9}\)+x:\(\frac{2}{7}\)=252
x+x*\(\frac{9}{4}\)+x*\(\frac{7}{2}\)=252
x*(1+\(\frac{9}{4}\)+\(\frac{7}{2}\))=252
x*\(\frac{27}{4}\)=252
x=252:\(\frac{27}{4}\)
x=\(\frac{112}{3}\)
Vậy x=\(\frac{112}{3}\)
Học tốt
\(x+x\times\frac{1}{2}\div\frac{2}{9}+x\div\frac{2}{7}=252\)
\(x\times1+x\times\frac{9}{4}+x\times\frac{7}{2}=252\)
\(x\times\left(1+\frac{9}{4}+\frac{7}{2}\right)=252\)
\(x\times\frac{17}{4}=252\)
\(x=252\div\frac{17}{4}\)
\(x=252\times\frac{4}{17}\)
\(x=\frac{1008}{17}\)
Chắc sai =]]
