\(\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{3}{42}\)
\(=\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{1}{14}\)
\(=\dfrac{21\times13\times56}{17\times14\times14}\)
\(=\dfrac{3\times7\times13\times14\times2\times2}{17\times2\times7\times14}\)
\(=\dfrac{3\times13\times2}{17}\)
\(=\dfrac{78}{17}\)

\(\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{3}{42}=\dfrac{78}{17}\)

Giúpppp mìnhh vớiiiiiiiiiiiiiiiiiiiiiiiii nhanhhhhhhhhhhh lênnnnnnnnnnnnnnnnn

Nhanh rồi mình tích cho

a: \(\dfrac{6}{7}\cdot\dfrac{16}{15}\cdot\dfrac{7}{6}\cdot\dfrac{21}{32}=\dfrac{16}{32}\cdot\dfrac{21}{15}=\dfrac{1}{2}\cdot\dfrac{7}{5}=\dfrac{7}{10}\)

b: \(\dfrac{21}{17}\cdot\dfrac{13}{14}\cdot56\cdot\dfrac{3}{42}=\dfrac{21}{14}\cdot\dfrac{13}{17}\cdot\dfrac{1}{14}\cdot56=\dfrac{78}{17}\)

c: \(=\dfrac{11}{21}\left(\dfrac{7}{4}+\dfrac{5}{4}\right)=\dfrac{11}{21}\cdot3=\dfrac{11}{7}\)

b,21/17x13/14x56x3/42

=21/17x3/42x56x13/14

=21x3/17x42 x 56x13/14

=21x3/17x21x2 x 14x4x13/14

=3/17x2 x 4x13

=3/24 x 52=3x52/24

=3x52/3x8

=52/8=13/2

a, 6/7 x 16/15 x 7/6 x 21/32

=(6/7 x 7/6)x16/15x21/32

=16/15x21/32

=16x21/15x32

=16x3x7/3x5x16x2

=7/5x2=7/10

a. (+18) + (+2)= 20

b. (-3)+13= 11

c. (-12)+(-21)=-33

d. (-30)+(-23)=-53

e. -52+102=50

f. 88+(-23)=65

g. 13+|-13|=26

h. -43-26=-69

k. (-89)-9=-98

m. -56+|-32|=-24

n. 40 -|-14|=26

o. |-4|+|+15|=19

p. |30|-|-17|=13

0.5

Hôm nay olm.vn sẽ hướng dẫn các em giải dạng toán nâng cao cấu trúc thi hsg, violympic  tính nhanh tổng các phân số mà tử số bằng tổng hai thừa số dưới mẫu:

Kiến thức cần nhớ:  \(\dfrac{a}{b.c}\)  trong đó a = b + c

+ Tách từng phân số thanh tổng hai phân số :

 \(\dfrac{a}{b.c}\) = \(\dfrac{b+c}{b.c}\) = \(\dfrac{1}{b}+\dfrac{1}{c}\)

+ Triệt tiêu các hạng tử giống nhau.

+ Thu gọn ta được tổng cần tính                               

  \(\dfrac{2}{6}+\dfrac{9}{20}-\dfrac{11}{30}+\dfrac{13}{42}-\dfrac{15}{56}+\dfrac{17}{72}-\dfrac{19}{90}+\dfrac{21}{110}-\dfrac{23}{132}\)

=\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{5}\)-(\(\dfrac{1}{5}+\dfrac{1}{6}\))+\(\dfrac{1}{6}\)+\(\dfrac{1}{7}\)-(\(\dfrac{1}{7}\)+\(\dfrac{1}{8}\))+\(\dfrac{1}{8}\) +\(\dfrac{1}{9}\)-(\(\dfrac{1}{9}\)+\(\dfrac{1}{10}\))+\(\dfrac{1}{10}\)+\(\dfrac{1}{11}\)-(\(\dfrac{1}{11}\)+\(\dfrac{1}{12}\))

= \(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{5}\)-\(\dfrac{1}{5}\)-\(\dfrac{1}{6}\)+\(\dfrac{1}{6}\)+\(\dfrac{1}{7}\)-\(\dfrac{1}{7}\)-\(\dfrac{1}{8}\)+\(\dfrac{1}{8}\)+\(\dfrac{1}{9}\)-\(\dfrac{1}{9}\)-\(\dfrac{1}{10}\)+\(\dfrac{1}{10}\)+\(\dfrac{1}{11}\)-\(\dfrac{1}{11}\)-\(\dfrac{1}{12}\)

= \(\dfrac{1}{3}\)+\(\dfrac{1}{4}\) - \(\dfrac{1}{12}\)

= \(\dfrac{4}{12}+\dfrac{3}{12}-\dfrac{1}{12}\)

= \(\dfrac{1}{2}\)

12) 17 – 11 – 14 – (-39)

=17-11-14+39

=6-14+39

=-8+39

=31

13) −127 - 18.( 5 - 6)

=-127-18.1

=-145
14) 100 + (+430) + 2145 + (-530)

=530+2145-530

=(530-530)+2145

=0+2145

=2145
15) (+12).13 + 13.(-22)

=13.[12+(-22)]

=13.(-10)

=-130
16) {[14 : (-2)] + 7} : 2012

={-7+7}:2012

=0:2012

=0
17) 13 – 18 – (- 42) - 15

=13-18+42-15

=-5+42-15

=37-15

=22
18) 369 – 4[(-5) + 4.(-8)]

=369-4[-5+(-32)]

=369-4(-37)

=369+148

=517
19) (-12).(-13) +13.(-29)

=12.13+13.(-29)=13.[12+(-29)]=13.(-17)=-221

20) 125 – 4[ 3 – 7.(-2) ]

=125-4[3+14]

=125-4.17

=125-68

=57
21) (-14).9 – 13.(-9)

=(-14).9+13.9

=9.[-14+13]

=9.(-1)

=-9

âm 9 nha bạn
 

1+2+3+4+....-56+56+48.......-23+56+586=6928

=6978 nha bn 

6928 bn nhé