a)

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+2010\right)=2029099\\ 2011.x+\left(1+2+3+...+2010\right)=2029099\\ 2011.x+2021055=2029099\\ 2011.x=2029099-2021055\\ 2011.x=8044\\ x=8044:2011\\ x=4\)

b)

\(2+4+6+...+2x=210\\ 2.\left(1+2+3+...+x\right)=210\\ 1+2+3+...+x=210:2\\ 1+2+3+...+x=105\\ \dfrac{x.\left(x+1\right)}{2}=105\\ x.\left(x+1\right)=105.2\\ x\left(x+1\right)=210\\ x.\left(x+1\right)=14.15\\\Rightarrow x=14\)

\(\left(1-\dfrac{1}{2}\right)\left(1-\dfrac{1}{3}\right)\left(1-\dfrac{1}{4}\right)...\left(1-\dfrac{1}{a+1}\right)\\ =\dfrac{1}{2}.\dfrac{2}{3}.\dfrac{3}{4}.....\dfrac{a}{a+1}\\ =\dfrac{1}{a+1}\)

3, 5, 7

\(x-25\%x=\dfrac{1}{2}\\ x-\dfrac{1}{4}x=\dfrac{1}{2}\\ x\cdot\left(1-\dfrac{1}{4}\right)=\dfrac{1}{2}\\ x\cdot\dfrac{3}{4}=\dfrac{1}{2}\\ x=\dfrac{1}{2}:\dfrac{3}{4}\\ x=\dfrac{2}{3}\)

\(A=\dfrac{\dfrac{2017}{2}+\dfrac{2017}{3}+\dfrac{2017}{4}+...+\dfrac{2017}{2018}}{\dfrac{2017}{1}+\dfrac{2016}{2}+...+\dfrac{1}{2017}}\)

Đặt \(\dfrac{2017}{1}+\dfrac{2016}{2}+...+\dfrac{1}{2017}\) là B

\(B=\dfrac{2017}{1}+\dfrac{2016}{2}+...+\dfrac{1}{2017}\\ =\dfrac{2017}{1}+1+\dfrac{2016}{2}+1+...+\dfrac{1}{2017}+1-2017\\ =\dfrac{2018}{1}+\dfrac{2018}{2}+...+\dfrac{2018}{2017}-2017\\ =\dfrac{2018}{2}+\dfrac{2018}{3}+...+\dfrac{2018}{2017}+\left(2018-2017\right)\\ =\dfrac{2018}{2}+\dfrac{2018}{3}+...+\dfrac{2018}{2017}+1\\ =\dfrac{2018}{2}+\dfrac{2018}{3}+...+\dfrac{2018}{2017}+\dfrac{2018}{2018}\\ =2018.\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2018}\right)\)

\(A=\dfrac{\dfrac{2017}{2}+\dfrac{2017}{3}+...+\dfrac{2017}{2018}}{2018\cdot\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2018}\right)}\\ =\dfrac{2017.\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2018}\right)}{2018.\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2018}\right)}\\ =\dfrac{2017}{2018}\)

a là số chia \(\Rightarrow a>28\)

1960 chia a dư 28 \(\Rightarrow\left(1960-28\right)⋮a\) hay \(1932⋮a\)

2002 chia a dư 28 \(\Rightarrow\left(2002-28\right)⋮a\) hay \(1974⋮a\)

a) 40

Nhi kp với mk đi

a) \(\widehat{BOC}\), \(\widehat{AOF}\), \(\widehat{DOB}\),\(\widehat{EOA}\),\(\widehat{DOA}\)

b) \(\widehat{EOA}\), \(\widehat{DOB}\)

87x4=348

45+24=69

 4x97+96x97

=(4+96)x97

=100x97

=9700