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

\(\dfrac{-4}{12}-\left(-\dfrac{13}{39}-0.25\right)+0.75\)

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

=1

x : 0,1 = 12

x x 10 = 12

x = 12 : 10

x = 1,2

--------------------------------------------

4 : 0,25 + 320 x 0,5 + 3: 0,125

= 4 x 4 + 320 : 2 + 3 x 8

= 16 + 160 + 24

= 160 + (16 + 24)

= 160 + 40

= 200

=10650

sai thì thôi nha bạn

bạn đúng rồi mà

(60 x 213 x 10): 12 

=(60 x 10 x213):12

=(600x213):12

=127800:12

=10650

 k mik nha ♥

a, 10 -12 - 8

= 10 - (12 + 8 )

= 10 - 20 = -10

b, 4-(-15)-5+6

= 4+15-5+6

= (4+6) + (15-5)

= 10+10=20

c, 2-12-4-6

= (2-12)-(4+6)

= (-10) - 10

=-20

d, -45-5-(-12)+8

= -45-5+12+8

= [(-45)-5]+(12+8)

= (-50)+20

= -30

\(a.10-12-8\\ =10+\left(-12-8\right)\\ =10+\left(-20\right)=-10\\ b.4-\left(-15\right)-5+6\\ =4+5-5+6\\ =\left(4+6\right)+\left(15-5\right)\\ =10+10=20\\ c.2-12-4-6\\ =\left(2-12\right)+\left(-4-6\right)\\ =-10+\left(-10\right)=-20\\ d.-45-5-\left(-12\right)+8\\ =-45-5+12+8\\ =\left(-45-5\right)+\left(12+8\right)\\ =-50+20=-30\)

12 . 19 + 12

= 12 . 19 + 12 . 1

= 12 . ( 19 + 1 )

= 12 . 20

= 240

\(12\cdot19+12=12\left(19+1\right)=12\cdot20=240\)

Mình cảm ơn trước nha

 A= 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 
=1/(1.2)+1/(2.3)+1/(3.4)+1/(4.5) +1/(5.6)+1/(6.7)+1/(7.8) +1/(8.9)+1/(9.10) 
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5.+1/5-1/6... +1/9-1/10 
=1-1/10 
=9/10

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\)

\(A=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{9.10}\)

\(A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\)

\(A=\frac{1}{1}-\frac{1}{10}=\frac{10}{10}-\frac{1}{10}=\frac{9}{10}\)

13-12+11+10-9+8-7-6+5-4+3+2-1
=13-(12+1) -(11+2)-(10+3)-(9+4)-(8+5) +(7+6)
=13-13-13-13-13-13+13
=0-0-0-0-0-0+13
=0+13
=13

sửa lại đề bài đi : Tính hợp lí:13 - 12 + 11 + 10 - 9 + 8 - 7 - 6 + 5 - 4 + 3 +2 - 1

:A