a) -2021.371+2021-(-629)

=2021.(-371)+2021+629

=2021.[-371+1]+629

=2021.(-370)+629

=-747770+629

=-747141

b) 957.(-37)-137.(-957)

=957.(-37)+137.957

=957.[-37+137]

=957.100

=95700

d) (451-527)+(527-741-451)

=451-527+527-741-451

=(451-451)+(-527+527)-741

=0+0-741

=-741

e) (-632+129)-(-17-632+129)

=-632+129+17+632-129

=(-632+632)+(129-12)+17

=0+0+17

=17

thế còn câu f thì sao hả hội con

a, \(\dfrac{10}{17}\) + \(\dfrac{5}{-13}\) - \(\dfrac{11}{25}\) + \(\dfrac{7}{17}\) - \(\dfrac{8}{13}\)

= ( \(\dfrac{10}{17}\) + \(\dfrac{7}{17}\)) - ( \(\dfrac{5}{13}\) + \(\dfrac{8}{13}\)) - \(\dfrac{11}{25}\)

= \(\dfrac{17}{17}\) - \(\dfrac{13}{13}\) - \(\dfrac{11}{25}\)

= 1 - 1 - \(\dfrac{11}{25}\)

= - \(\dfrac{11}{25}\)

b, 0,3 - \(\dfrac{93}{7}\) - 70% - \(\dfrac{4}{7}\)

= 0,3 - 0,7 - ( \(\dfrac{93}{7}+\dfrac{4}{7}\))

= - 0,4 - \(\dfrac{97}{7}\)
= - \(\dfrac{2}{5}\) - \(\dfrac{97}{7}\)

= - \(\dfrac{499}{35}\)

c, \(\dfrac{1}{8}\) + \(\dfrac{1}{24}\) + \(\dfrac{1}{48}\)+ ...+ \(\dfrac{1}{2400}\)

= \(\dfrac{1}{2\times4}\)  +\(\dfrac{1}{4\times6}\) + \(\dfrac{1}{6\times8}\) +...+ \(\dfrac{1}{48\times50}\)

= \(\dfrac{1}{2}\) \(\times\) ( \(\dfrac{2}{2\times4}\) +\(\dfrac{2}{4\times6}\)+ \(\dfrac{2}{6\times8}\) +...+ \(\dfrac{2}{48\times50}\))

= \(\dfrac{1}{2}\) \(\times\) ( \(\dfrac{1}{2}\) - \(\dfrac{1}{4}\) + \(\dfrac{1}{4}\) - \(\dfrac{1}{6}\) + \(\dfrac{1}{6}\) - \(\dfrac{1}{8}\) +...+ \(\dfrac{1}{48}\) - \(\dfrac{1}{50}\))

= \(\dfrac{1}{2}\) \(\times\) ( \(\dfrac{1}{2}\) - \(\dfrac{1}{50}\))

= \(\dfrac{1}{2}\) \(\times\) \(\dfrac{12}{25}\)

= \(\dfrac{6}{25}\)

Chọn đáp án B : 49736

chọn đáp án B

x + 630 = 1218

        x  =  1218- 630 

        x = 588

x+630=586+632

=>x=586+632-630=588

586 ĐÚNG

Giúp mình với mình đang cần gấp!!!

=> D + 49 = (1/49 + 1) + (2/48 + 1) +... (49/1 + 1)

= 50/1 + 50/2 + ... + 50/49

= 50(1/2+1/3+...+1/49) + 50

=> D = 50(1/2 + 1/3 +... + 1/49) + 1

= 50(1/2 + 1/3 +... + 1/49 + 1/50)

=> C/D = 1/50

A=625

B=10000

1+12=13

giup mih voi

dell bt

phải k mình mới làm

a)35.18-5.7.28

=35.18-35.28

=35.(18-28)

=35.(-10)

=-350

NHỚ K ĐÓ

\(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{100}}\\ 2A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{99}}\\ 2A-A=\left(1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{99}}\right)-\left(\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{100}}\right)\\ A=1-\dfrac{1}{2^{100}}\)

\(E=\dfrac{3^2}{2\cdot4}+\dfrac{3^2}{4\cdot6}+...+\dfrac{3^2}{198\cdot200}\\ =3^2\cdot\left(\dfrac{1}{2\cdot4}+\dfrac{1}{4\cdot6}+...+\dfrac{1}{198\cdot200}\right)\\ =9\cdot\dfrac{1}{2}\cdot\left(\dfrac{2}{2\cdot4}+\dfrac{2}{4\cdot6}+...+\dfrac{2}{198\cdot200}\right)\\ =\dfrac{9}{2}\cdot\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+...+\dfrac{1}{198}-\dfrac{1}{200}\right)\\ =\dfrac{9}{2}\cdot\left(\dfrac{1}{2}-\dfrac{1}{200}\right)\\ =\dfrac{9}{2}\cdot\dfrac{99}{200}\\ =\dfrac{891}{400}\)

\(B=1\cdot2+2\cdot3+3\cdot4+...+48\cdot49\\ 3B=1\cdot2\cdot3+2\cdot3\cdot3+3\cdot4\cdot3+...+48\cdot49\cdot3\\ 3B=1\cdot2\cdot\left(3-0\right)+2\cdot3\cdot\left(4-1\right)+3\cdot4\cdot\left(5-2\right)+...+48\cdot49\cdot\left(50-47\right)\\ 3B=1\cdot2\cdot3-0\cdot1\cdot2+2\cdot3\cdot4-1\cdot2\cdot3+3\cdot4\cdot5-2\cdot3\cdot4+...+48\cdot49\cdot50-47\cdot48\cdot49\\ 3B=-0\cdot1\cdot2+\left(1\cdot2\cdot3-1\cdot2\cdot3\right)+\left(2\cdot3\cdot4-2\cdot3\cdot4\right)+...+\left(47\cdot48\cdot49-47\cdot48\cdot49\right)+48\cdot49\cdot50\\ =0+48\cdot49\cdot50\\ =48\cdot49\cdot50\\ B=\dfrac{48\cdot49\cdot50}{3}\\ B=39200\)

a: \(A=\dfrac{\left(37+12\right)\left(37^2+12^2-37\cdot12\right)}{49-37\cdot12}\)

\(=\dfrac{49\cdot1069}{49-37\cdot12}\simeq-132.61\)

b: \(=\dfrac{\left(52-48\right)\left(52^2+48^2+52\cdot48\right)}{4+52\cdot48}\)

\(=\dfrac{4\cdot7504}{4+52\cdot48}=\dfrac{7504}{625}\)