30+12+-20-(-12)

=30+12+-20+12

=(-20+30)+(12+12)

=10+24

=34

30+12+(-20)-(-12)

=12+(-12)+30+(-20)

=0+10

=10

ai k mình mình k lại

34 đây là kết quả các bạn k mình nha thank you nhiều

\(=30+12-20+12\)

\(=42-20+12\)

\(=22+12\)

\(=34\)

=34 nha bn

30+12(-20)-(-12)

=12+(-12)+30-(-20)

=0+10

=10

15.141+59.15=2115+885=3000

20-[30-(5-1²)]=20-[30-(5-1)]=20-[30-4)]=20-26=.....chỗ này đề bài sai nha bn

20-[30-(5-1^2)]=20-[30-(5-1)^2]=20-[30-4^2]=20-[30-16]=20-14=6

b: \(=15\left(141+19\right)=15\cdot160=24000\)

c: \(=2^3\cdot\left(17-14\right)=8\cdot3=24\)

a,  3 . 5 2 - 16 : 2 2 = 3.25  - 16:4 = 75 - 4 = 71

b, 15.141 + 59.15 = 15.(141+59) = 15.200 = 3000

c,  2 3 . 17 - 2 3 . 14 = 8.17 - 8.14 = 8.(17 - 14) = 8.3 = 24

d, 20 - 30 - 5 - 1 2 = 20 - 30 - 4 2 = 20 - (30 - 16) = 20 - 14 = 6

=2/12=1/6

-2/12 = -1/6

\(\dfrac{-2}{12}\)

a,  5 . 2 2 - 18 : 3 2

= 5.4 – 18:9

= 20 – 2 = 18

b, 17.85+15.17 – 120

= 1445+255 – 120

= 1580

c,  2 3 . 17 - 2 3 . 14

=  2 3 . ( 17 - 14 ) = 8.3 = 24

d, 20 – [30 –  5 - 1 2 ]

= 20 – (30 – 16) = 6

 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 
=1/(2.3)+1/(3.4)+1/(4.5) + 1/(5.6)+ 1/(6.7)+1/(7.8)
=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 
=1-1/8 
=7/8

= 1/(2.3) + 1/(3.4) + 1/(4.5) + 1/(5.6) + 1/(6.7) + 1/(7.8)

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

= 1/2 - 1/8

= 3/8

Ta có: \(\dfrac{8}{9}-\dfrac{1}{72}-\dfrac{1}{56}-\dfrac{1}{42}-\dfrac{1}{30}-\dfrac{1}{20}-\dfrac{1}{12}-\dfrac{1}{6}-\dfrac{1}{2}\)

\(=\dfrac{8}{9}-\left(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}\right)\)

\(=\dfrac{8}{9}-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}\right)\)

\(=\dfrac{8}{9}-\left(1-\dfrac{1}{9}\right)\)

\(=\dfrac{8}{9}-\dfrac{8}{9}=0\)