86342 58 1488 283 514 502 38

165048

Nhiều trẻ trâu quá

\(2^4-50:25+13.7\)

\(=16-50:25+13.7\)

\(=16-2+91\)

\(=14+91\)

\(=105\)

\(a,-\dfrac{4}{7}-x=\dfrac{3}{5}-2x\\ \Leftrightarrow x=\dfrac{41}{35}\)

\(b,\dfrac{5}{7}-\dfrac{1}{13}+\dfrac{1}{4}=\dfrac{31}{2}-x\\ \Leftrightarrow x=\dfrac{5319}{364}\)

\(1+1=2\)

2

Câu a. 

\(2^4-50:25+13.7=16-2+91=105\)

Câu b.

\(4.\left\{3^2.\left[\left(5^2+2^3\right):11^1\right]-26\right\}+2002\)

\(=4.\left\{9.\left[\left(25+8\right):11\right]-26\right\}+2002\)

\(=4.\left[9.\left(33:11\right)-26\right]+2002\)

\(=4.\left(9.3-26\right)+2002=4.\left(27-26\right)+2002=4.1+2002=2006\)

1x 2 + 2 x 3 + 3 x 4 + ...+ 99 x 100

Ta có: 

1 x 2 x 3                                           = 1 x 2 x 3

2 x 3 x 3     = 2 x 3 x ( 4 - 1)             = 2 x 3 x 4 -  1 x 2 x 3

3 x 4 x 3     =  3 x 4 x ( 5 - 2)            = 3 x 4 x 5 -   2 x 3 x 4 

........................................................= ........................................

99 x 100 x 3 = 99 x 100 x (101 - 98)  = 99 x 100 x 101 - 99 x 100 x 98

Cộng vế với vế ta có:

1 x 2 x 3 + 2 x 3 x 3 + 3 x 4 x 3 +...+ 99 x 100 x 3 = 99 x100 x 101

(1 x 2 + 2 x 3 + 3 x 4 +...+ 99 x 100) x 3 =  99 x 100 x 101 

1 x 2 + 2 x 3 + 3 x 4 +...+ 99 x 100 = \(\dfrac{99\times100\times101}{3}\)

1 x 2 + 2 x 3 + 3 x 4 + ....+ 99 x 100 = 333300

333300

a, \(4320:9-8640:18+750\)

\(=4320:9-(8640:2):(18:2)+750\)

\(=4320:9-4320:9+750\)

\(=(4320-4320):9+750\)

\(=0:9+750=0+750=750\)

a, $4320:9-8640:18+750$

$=4320:9-(8640:2):(18:2)+750$

$=4320:9-4320:9+750$

$=(4320-4320):9+750$

$=0:9+750=0+750=750$

a, 4320 : 9 - 8640 : 18 + 750

     = 4320 : 9 - (8640 : 2) : 9 + 750

    =   4320 : 9 - 4320 : 9  + 750

    = 0 + 750

     = 750

\(\dfrac{23}{5}-x=-\dfrac{1}{6}+\dfrac{1}{2}\)

\(=>\dfrac{23}{5}-x=\dfrac{1}{3}\)

\(=>x=\dfrac{23}{5}-\dfrac{1}{3}\)

\(=>x=\dfrac{64}{15}\)

\(\dfrac{23}{5}-x=-\dfrac{1}{6}+\dfrac{1}{2}\\ =>\dfrac{23}{5}-x=\dfrac{1}{3}\\ =>x=\dfrac{23}{5}-\dfrac{1}{3}\\ =>x=\dfrac{64}{15}\)