\(\left(x+1\right)+\left(x+3\right)+...+\left(x+99\right)=5100\)

\(\Leftrightarrow50x+\frac{\left[\left(99-1\right):2+1\right]\left(99+1\right)}{2}=5100\)

\(\Leftrightarrow50x+2500=5100\)

\(\Leftrightarrow50x=2600\)

\(\Leftrightarrow x=52\)

Vậy ...

\(\left(x+1\right)+\left(x+3\right)+...+\left(x+99\right)=5100.\)

\(\Leftrightarrow x+1+x+3+...+x+99=5100.\)'

\(\Leftrightarrow\left(x+x+...+x\right)+\left(1+3+...+99\right)=5100\)

            50 số hạng x                   50 số hạng

\(\Leftrightarrow50x+\frac{\left(1+99\right)\cdot50}{2}=5100\)

\(\Leftrightarrow50x=5100-2500=2600\)

\(\Leftrightarrow x=52\)

Vậy x = 52

Học tốt nhé ^3^

nhanh lên các bạn

a)(x+1)+(x+2)+...+(x+30)=795

(x+x+...+x)+(1+2+3+...+30)=795

30x+465=795

30x=795-465

30x=330

x=330/30

x=11

b)(x+1)+(x+3)+...+(x+99)=5100

(x+x+...+x)+(1+3+...+99)=5100

50x+2500=5100

50x=5100-2500

50x=2600

x=2600/50

x=52

4) (x+1)+(x+2)+(x+3)+....+(x+30)=795

<=> (x+x+x+...+x)+(1+2+3+....+30)=795

<=> 30x+\(\frac{\left(30+1\right)\cdot30}{2}=795\)

<=> 30x+465=795

<=> 30x=330

<=> x=11

Vậy x=11

5) (x+1)+(x+3)+(x+5)+...+(x+99)=5100

<=> (x+x+x+...+x)+\(\frac{\left(99+1\right)\cdot50}{2}=5100\)

<=> 50x+2500=5100

<=> 50x=2600

<=> x=52

Vậy x=52

\(a.15-\left|x-3\right|=7\)

\(\Rightarrow\left|x-3\right|=8\)

\(\Rightarrow\orbr{\begin{cases}x-3=8\\x-3=-8\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=11\\x=-5\end{cases}}\)

\(b.x-\left(17-x\right)=x-10\)

\(\Rightarrow17-x=x-x+10\)

\(\Rightarrow17-x=10\)

\(\Rightarrow x=7\)

a) 15 - |x - 3| = 7

|x - 3| = 15 - 7 

|x - 3| = 8

* x - 3 = 8

x = 8 + 3

x = 11 

* x - 3 = -8

x = -8 + 3

x = -5

    vậy x thuộc {11; -5}

b) x - (17 - x) = x - 10

=> 2x - 17 = x - 7

=> 2x - x = 17 - 7

=> x = 10

    vậy x = 10

không biết giải

2001 

____

1991

1/1*2+1/2*3+1/3*4+1/4*5+...1/99+100