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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
(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 = \(\frac{284}{3}\)
x = 99 x a -99= 99 x (a-1)= 99 x (1001-1)= 99 x 1000= 99000.
\(\text{K - 2016 = }\frac{\text{1 + ( 1 + 2 ) + ( 1 + 2 + 3 ) + ... + ( 1 + 2 + 3 + ... + 2017 )}}{\text{2017 x 1 + 2016 x 2 + 2015 x 3 + ... + 2 x 2016 + 1 x 2017}}\)
a)\(\frac{5}{9}\times x-1=\frac{8}{9}\)
\(\frac{5}{9}\times x=\frac{8}{9}+1\)
\(\frac{5}{9}\times x=\frac{17}{9}\)
\(x=\frac{17}{9}:\frac{5}{9}\)
\(x=\frac{17}{5}\)
Ta có : (x + 2) + (x + 5) + (x + 8) + ...... + (x + 32) = 198
<=> (x + x + x + ...... + x) + (2 + 5 + 8 + ....... + 32) = 198
<=> 11x + 187 = 198
=> 11x = 198 - 187
=> 11x = 11
=> x = 1