28+49+15=
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A)
-65.(87-17)-87.(17-65)
=-65.87-(-65).17-87.17-87.(-65)
=-(-65).17-87.17
=65.17-87.17
=17.(65-87)
=17.(-22)
=-374
B)
72.(28-49)+28.(-49-72)
= 72.28-72.49+28.(-49)-28.72
= -72.49+28.(-49)
= 72.(-49)+28.(-49)
= (-49).(72+28)
= -49.100
=-4900
C)
18-(-27)+63-(63+27)
= 18+27+63-63-27
= 45+0-27
= 45+(-27)
=45-27
=18
KICK MÌNH NHÁ

\(\left(128-49\right)+\left(-51-28\right)\)
\(=128-49-51-28\)
\(=\left(128-28\right)-\left(49+51\right)\)
\(=100-100=0\)

a) \(\dfrac{3}{10}\)
b) \(\dfrac{9}{28}\)
c) \(\dfrac{88}{195}\)

72x(28-49)+28x(-49-72)
=72x(-21)+28x(-121)
=-1512+(-3388)
=-49900
Có 2 cách hiểu
+ ) 72x( 28 - 49 ) + 28x( -49 - 72)
= 72x . 28 - 72x . 49 - 28x . 49 - 28x . 72
= -72x . 49 - 28x . 49
= 49 . ( - 100x )
+) 72 . ( 28 - 49 ) + 28 . ( -49 - 72 )
= 72 . 28 - 72 . 49 -28 . 49 - 28 . 72
= -72 . 49 -28 . 49
= 49 . ( -100 ) = -4900

a ) 5 . ( - 2 ) . ( - 3 )
= ( - 10 ) . ( - 3 )
= 30
b ) ( - 20 ) + ( - 12 ) - ( - 4 )
= ( - 20 ) + ( - 12 ) + 4
= ( -20 ) + [ ( - 12 ) + 4 ]
= ( - 20 ) + ( - 8 )
= - 28
c . 78 . 45 - 145 . 78
= 78 . ( 45 - 145 )
= 78 . ( - 100 )
= - 7800

#)Giải :
Bài 1 :
\(A=\frac{15}{6.16}+\frac{15}{16.26}+\frac{15}{26.36}\)
\(A=3\left(\frac{5}{6.16}+\frac{5}{16.26}+\frac{5}{26.36}\right)\)
\(A=3\left(\frac{1}{6}-\frac{1}{16}+\frac{1}{16}-\frac{1}{26}+\frac{1}{26}-\frac{1}{36}\right)\)
\(A=3\left(\frac{1}{6}-\frac{1}{36}\right)\)
\(A=3.\frac{5}{36}\)
\(A=\frac{15}{36}\)
\(B=\frac{33}{6.16}-\frac{63}{16.26}+\frac{93}{26.36}\)
\(B=\frac{3.11}{6.16}-\frac{3.21}{16.26}+\frac{3.31}{26.36}\)
\(B=\frac{1}{2.16}.11+\frac{1}{2.16}.\frac{3.21}{13}+\frac{3.31}{26.36}\)
\(B=\frac{1}{32}.\frac{143-63}{13}+\frac{3.31}{26.12.3}\)
\(B=\frac{1}{32}.\frac{80}{13}+\frac{31}{36.12}\)
\(B=\frac{5}{26}+\frac{31}{26.12}=\frac{60+31}{26.12}=\frac{91}{26.12}=\frac{13.7}{13.2.12}=\frac{7}{24}\)
Bài 2 :
a)\(28.157-28.267+28.10\)
\(=28\left(157-267+10\right)\)
\(=28.-100\)
\(=-2800\)
b)\(\left(-5\right).4.\left(-2\right).23.\left(-25\right)\)
\(=\left[4.\left(-25\right)\right].\left[\left(-5\right).2\right].23\)
\(=\left(-100\right).\left(-10\right).23\)
\(=23000\)
2)
28 . 157 - 28 .267 + 28.10
=28.( 157 - 267 + 10 )
= 28 . -100
= -2800
3)
[(-2).(-5)]. 4 .-25.23
= 10 . -100 .23
=-23000
còn câu 1 mik suy nghĩ đã

a) ( -12 ) + ( - 9 ) + 121 + | -20 |
= ( - 21 ) + 121 + 20
= [ ( - 21) + 121 ] + 20
= 100 + 20
= 120
b) 49.125 - 49 .25
= 49 .( 125 -25 )
= 49. 100
= 4900
c) 20 -[ 30 - ( 5- 1)2 ]
= 20 - ( 30 - 42 )
= 20 - ( 30 - 16 )
= 20 - 14
= 6
d) 28 . 76 + 44.28 -28.20
= 28 .( 76 + 44 -20)
= 28 . 100
= 2800

a)
\( 49.(51 - 4) - 51.(49 + 4)\)
\(=49.51-49.4-51.49-51.4\)
\(=49.(51-4-51)-51.4\)
\(=49.(-4)-51.4\)
\(=4.(-49-51)\)
\(=4.(-100)\)
\(=-400\)
b)
\( 71.64 + 32.(-7) - 13.32\)
\(=71.32.2+32.(-7)-13.32\)
\(=142.32+32.(-7)-13.32\)
\(=32.(142-7-13)\)
\(=32.122\)
\(=3904\)
c)
\( 11 + (-13) + 15 + (-17) + ... + 59 + (-61)\)
\(=(-2)+(-2)+...+(-2)\)
\(=(-2).13\)
\(=-26\)
=87
28 + 49 + 15
= 77+ 15
= 92