\(a.=\dfrac{2019}{2020}\times\left(\dfrac{4}{11}+\dfrac{5}{11}+\dfrac{2}{11}\right)\\ =\dfrac{2019}{2020}\times1=\dfrac{2019}{2020}\\ b.=\dfrac{25}{27}\times\left(\dfrac{17}{14}-\dfrac{1}{14}-\dfrac{2}{14}\right)\\ =\dfrac{25}{27}\times1=\dfrac{25}{27}\)

Thanks mik chữ cũng hơi ẩu

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\(x+\left(x+1\right)+\left(x+2\right)+....+13+14=14\Leftrightarrow x+\left(x+1\right)+....+13\Leftrightarrow x=-13\)

\(25+24+23+....+x+\left(x-1\right)+\left(x-2\right)=25\Leftrightarrow24+....+\left(x-2\right)=0\Leftrightarrow x-2=-24\)

\(\Leftrightarrow x=-22\)

bạn làm rõ hơn đi

a: =>14x+2*(14*13/2)=14

=>14x+14*13=14

=>14x=-12*14

=>x=-12

b: =>3x+(0-1-2-3+1+2+...+25)=25

=>3x+4+...+25=25

=>3x+4+...+24=0

=>3x+(24-4+1)*28/2=0

=>3x+21*28/2=0

=>3x=-21*14

=>x=-7*14=-98

207 : {2³ . [(165 . 1²⁶⁰ - 128) : 14] +7}

=207 : {2³ . [(165 - 128)] : 14] +7}

=207 : {2³ . [ 37 : 14] +7}

=207 : {2³ . 2 +7}

=207 : 23 = 9

   207 : { 2³ x [ (165 x 1²⁶⁰ - 128 ) : 14 ] + 7 }

= 207 : { 8 x [ ( 165 x 1 - 128 ) :14 ] + 7 }

= 207 : { 8 x [ ( 165 - 128 ) : 14 ] + 7 }

= 207 : { 8 x [ 37 : 14 ] + 7 }

= 207 : { 8 x 2,642857142857143 + 7 }

= 207 : { 21,14285714286 + 7 }

= 207 : 28,14285714286

= 7.35532994924

Ta có : \(14-\left(25-x\right)+\left(-14+50\right).14-\left(25-x\right)+\left(-14+50\right)\)

\(=14-25+x+36.14-25+x-14+50\)

\(=2x+36.14=2x+504\)

Giải:

\(14-\left(25-x\right)+\left(-14+50\right).14-\left(25-x\right)+\left(-14+50\right)\) 

\(=14-25+x+\left(-14.14+50.14\right)-25+x-14+50\) 

\(=\left(14-14\right)+\left(-25-25+50\right)+\left(x+x\right)+\left(-196+700\right)\) 

\(=0+0+2x+504\) 

\(=2x+504\) 

Chúc bạn học tốt!