bằng 21 nha bn

yick mk nha

237 + ( 49 - 237 ) - ( 49 - 21 )

= 237 + 49 - 237 - 49 + 21

= ( 237 - 237 ) + ( 49 - 49 ) + 21

= 0 + 0 + 21

= 21

125 = 100 + 25

21 = 22 - 1 

a) 100+25x100+1
b) 20+1x50-1

a) 125 . 101 = 125 . (100 + 1) = 125 . 100 + 125 . 1

= 12 500 + 125 = 12 625

b) 21 . 49 = 21 . (50 - 1) = 21 . 50 - 21 . 1

= 1 050 - 21 = 1 029

Bài giải

Ta có: \(\frac{49+\left(-49\right).\left(-2\right)}{7.21}\)

= \(\frac{49.1+49.2}{7.21}\)

= \(\frac{49.\left(1+2\right)}{7.21}\)

= \(\frac{49.3}{7.21}\)

= \(\frac{7.7.3}{7.7.3}\)

= \(1\)

53 x 39 + 49 x 39 - 53 x 21 - 47 x 21

= 39 x ( 53 + 49 ) - 21 x ( 53 - 47 )

= 39 x 102 - 21 x 6

= 3978 - 136

= 3842

53 x 39 + 49 x 39 - 53 x 21 - 47 x 21

= 39 x ( 53 + 49 ) - 21 x ( 53 - 47 )

= 39 x 102 - 21 x 6

= 3978 - 136

= 3842

a) |-15+6| = |-9| = 9

b) |-25 + (-17)| = |-42| =  42

c) | -36 +  15| = |-21| = 21

d) |-21 + 49| = | 48| = 48

e) |-21+49| = |48| = 48 

g) |43 + (-28) | = | 15|  = 15

h) |-23 + 33|  = |10| = 10

i) |-46 + (-29) | = | -75| = 75

=>4/x=y/21=4/7

=>x=7; y=12

– 25 . 21 + 25 . 72 + 49 . 25 = 2504

  Tk ik

=2504

Tk cho tui ik

350-x=49+2(3x-21)

49+2(3x-21)=350-x

2(3x-21)=350-x-49

2(3x-21)=301-x

6x-42=301-x

6x=301-x+42

343-x=6x

=>6x+x=343

=>7x=343

=>x=49

Hok tốt

K mk nha

350 - x = 49 + 2(3x - 21)

<=> 350 - x = 49 + 6x - 42 

<=> 350 - 49 + 42 = 6x + x

<=>  343 = 7x

=> x = 49