X x 2018 - 2018 = 2018 x 2019 - 4036
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Ta có : X x 2018 - 2018 = 2018 x 2019 - 4036
=> 2018 x (X - 1) = 2018 x (2019 - 2)
=> 2018 x (X - 1) = 2018 x 2017
Thấy X - 1 = 2017 => x = 2017 + 1 = 2018
Vậy x = ...
X x 2018 - 2018 = 2018 x 2019 - 4036
X x 2018 -2018 = 4070306
X x 2018 = 4070306 + 2018
X x 2018 = 4072324
X = 4072324 : 2018
X = 2018
Ta có : x = 99
=> 100 = x + 1
Thay vào A ta có : A = x2018 - 100x2017 + 100x2016 - ...... + 100x2 - 100x + 2019
=> A = x2018 - (x + 1)x2017 + (x + 1)x2016 - ...... + (x + 1)x2 - (x + 1)x + 2019
=> A = x2018 - x2018 - x2017 + x2017 + x2016 -.......+ x3 + x2 - x2 + x + 2019
=> A = x + 2019
=> A = 99 + 2019
=> A = 2118
P/s : ko cần ! :D
Theo đề bài ra ta có :
x = 99
Thay vào A ta có :
A = x2018 - 100x2017 + 100x2016 - ... + 100x2 - 100x + 2019
\(\Rightarrow\) A = x2018 - ( x + 1 ) x2017 + ( x + 1 ) x2016 - ... + ( x + 1 ) x2 - ( x + 1 ) x + 2019
\(\Rightarrow\) A = x2018 - x2018 - x2017 + x2017 + x2016- ... + x3 + x2 - x2 + x + 2019
\(\Rightarrow\) A = x + 2019
\(\Rightarrow\) A = 99 + 2019
\(\Rightarrow\) A = 2118
\(x\times2019-x=2018\times2018+2018\)
\(x\times\left(2019-1\right)=2018\times\left(2018+1\right)\)
\(x\times2018=2018\times2019\)
\(\Rightarrow x=2019\)
X x 2019 - x =2018 x 2018 + 2018
X x(2019-1) = 2018 x(2018 + 1)
X x 2018 = 2018 x 2019
=> X=2019
Vậy X=2019.
\(\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{1}{2019}x2018\)
\(=\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{2018}{2019}=2-\dfrac{2019}{2018}=\dfrac{2017}{2018}\)
\(\frac{x+2019}{x+2018}=\frac{4038}{4037}\)
\(\Rightarrow\left(x+2019\right)4037=\left(x+2018\right)4038\)
\(\Rightarrow4037x+\left(4037\times2019\right)=4038x+\left(4038\times2018\right)\)
\(\Rightarrow4037x+8150703=4038x+8148684\)
\(\Rightarrow4037x-4038x=-8150703+8148684\)
\(\Rightarrow-x=-2019\)
\(\Rightarrow x=2019\)
P/s: Số to kinh -_- Ko chắc đúng đâu.
26 x 84 + 74 x 85
= 26 x 84 + 74 x 84 + 74
= 84 x (26 + 74) + 74
= 84 x 100 + 74
= 840 + 74
= 914
\(\frac{2017\times2018+2019}{2019\times2018-2017}\)
= \(\frac{2019\times2018-2\times2018+2019}{2019\times2018-2017}\)
= \(\frac{2019\times2018-4036+2019}{2019\times2018-2017}\)
= \(\frac{2019\times2018-2017}{2019\times2018-2017}\)
= 1
`@` `\text {Ans}`
`\downarrow`
`a)`
`13/50 + 9% + 41/100 + 0,24`
`= 0,26 + 0,09 + 0,41 + 0,24`
`= (0,26 + 0,24) + (0,09 + 0,41)`
`= 0,5 + 0,5`
`= 1`
`b)`
`2018 \times 2020 - 1/2017 + 2018 \times 2019`
`= 2018 \times (2020 + 2019) - 1/2017`
`= 2018 \times 4039 - 1/2017`
`= 8150702`
`c)`
`1/2 + 1/6 + 1/12 + 1/20 +1/30 +1/42`
`=`\(\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}\)
`=`\(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{6}-\dfrac{1}{7}\)
`=`\(1-\dfrac{1}{7}\)
`= 6/7`
\(a,\dfrac{13}{50}+9\%+\dfrac{41}{100}+0,24\\ 0,26+0,09+0,41+0,24\\ =\left(0,26+0,24\right)+\left(0,09+0,41\right)\\ =0,5+0,5\\ =1\\ b,2018\times2020-\dfrac{1}{2017}+2018\times2019\\ =2018\times\left(2020+2019\right)-\dfrac{1}{2017}\\ =2018\times4039-\dfrac{1}{2017}\\ =3150702-\dfrac{1}{2017}\\ c,\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}\\ =1-\dfrac{1}{2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+\dfrac{1}{5\cdot6}+\dfrac{1}{6\cdot7}\\ =1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}.........+\dfrac{1}{6}-\dfrac{1}{7}\\ =1-\dfrac{1}{7}\\ =\dfrac{6}{7}\)
X =2018
X=2018
Học giỏi nhé--