=65-38-65+12+42

=(65-65)+12+42-38

=0+54-38

=16

65 +(- 38 ) + (  - 65 ) +12 - ( - 42 )

=65 - 38 - 65 + 12 + 42

=16

=65-38-65+12+42

=16

1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72

\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)\(+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{7}-\frac{1}{8}\)\(+\frac{1}{8}-\frac{1}{9}\)

\(=1-\frac{1}{9}\)

\(=\frac{8}{9}\)

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72

=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9

=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9

=1-1/9

=8/9

\(=\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{8.9}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{8}-\frac{1}{9}\)

\(=1-\frac{1}{9}\)

\(=\frac{8}{9}\)

Đú đởn ăn chơi học hành sa sút đến nỗi có bài toán đơn giản như zậy mà cũng phải hỏi !

40-41+42-43+44-45+46-47+48-49+50-51+52-53+54-55+56-57+58=

=40+(42-41)+(44-43)+(46-45)+(48-47)+(50-49)+(52-51)+(54-53)+(56-55)+(58-57)=49

chơi ff ko xin id

( 2x + 1) ³ = -0,001

(2x+1)³=(-0,1)³

=>2x+1=-0,1

2x=-0,1-1

2x=\(\frac{-1}{10}-\frac{10}{10}\)

2x=\(\frac{-11}{10}\)

x=\(\frac{-11}{10}:2\)

x=\(\frac{-11}{10}.\frac{1}{2}\)

x=\(\frac{-11}{20}\)

\(-2,5\times\left(x+\dfrac{1}{5}\right)=\dfrac{7}{5}\)

\(\Leftrightarrow x+\dfrac{1}{5}=\dfrac{7}{5}:\left(-2,5\right)\)

\(\Leftrightarrow x+\dfrac{1}{5}=\dfrac{7}{5}\times\left(-\dfrac{2}{5}\right)\)

\(\Leftrightarrow x+\dfrac{1}{5}=-\dfrac{14}{25}\)

\(\Leftrightarrow x=-\dfrac{19}{25}\)

\(-2,5\cdot\left(x+\dfrac{1}{5}\right)=\dfrac{7}{5}\)

\(x+\dfrac{1}{5}=\dfrac{7}{5}:\left(-2,5\right)\)

\(x+\dfrac{1}{5}=\dfrac{7}{5}\times\left(-\dfrac{2}{5}\right)\)

\(x+\dfrac{1}{5}=-\dfrac{14}{25}\)

\(x=-\dfrac{14}{25}-\dfrac{1}{5}\)

\(x=-\dfrac{19}{25}\)

x+1/5=7/5:(-5/2)
x= -14/25 -1/5
x= -19/25

Lời giải:

Vì $|x-2|\geq 0$ nên $4-2x\geq 0$

$\Leftrightarrow x\leq 2$
$\Rightarrow |x-2|=2-x$. Khi đó:

$2-x=4-2x$

$x=2$

|x-2|=4-2x (1)

ta có: |x-2|=x-2 nếu x-2 ≥0 thì x≥2

          |x-2|=-x+2 nếu x-2<0 thì x<2

với x≥2 thì pt (1) trở thành:

   x-2=4-2x

⇔x+2x=2+4

⇔3x=6

⇔x=2 (T/m)

với x<2 thì pt (1) trở thành:

-x+2=4-2x

⇔-x+2x=-2+4

⇔x=2 (Không T/m)

Vậy pt có tập nghiệm S={2}

ko bít

Đặt \(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{1024}\)

\(2A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{1024}\)

\(2A-A=\left(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{1024}\right)-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{1024}\right)\)

\(\Rightarrow A=1-\frac{1}{1024}=\frac{1023}{1024}\)

Đặt \(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+.....+\frac{1}{1024}\)

=> \(2A=1+\frac{1}{2}+\frac{1}{4}+.......+\frac{1}{512}\)

=> \(2A-A=1-\frac{1}{1024}\)

=> \(A=\frac{1023}{1024}\)