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a, -27 . 49 + 27 . ( -51 )
= -27 . 49 + ( -27 ). 51
= -27 ( 49 + 51 )
= -27 . 100
= -2700
b,38 . ( 28 - 15 ) - 28 . ( 38 - 15 )
= 38 . 28 - 38 . 15 - 28 . 38 - 15 . 28
= 38 . 28 - 28 . 38 - 38 . 15 - 15 . 28
= 38 . ( 28 - 28 ) - 15 . ( 38 - 28 )
= 0 - 15 . 10
= - 150
HOK TỐT
a,-27.49+27.(-51)=27.-49+27.(-51)=27.(-49+-51)=27.-100=-2700
b,38.(28-15)-28.(38-15)=38.28-38.15-28.38-28.15=38.(28-28)-15.(38-28)=38.0-15.10=0-150=-150
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Số phần tử của A là: (33-26):1+1=8 (số hạng)
vậy A= (33+26).8/2=236
[Giải:]
= (26 + 33) + (27 + 32) + (28 + 31) +(29 + 30)
= 59 + 59 + 59 + 59
= 59 . 4
= 236
[ Hoq chắc ]
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26 + 27 + 28 + 29 + 30 + 31 + 32 + 33
= (27+33) + ( 28+32) + (29+31) + ( 26 + 30)
= 60 + 60 + 60 + 66
= 60 + 60 + 60 + 60 + 6
= 4.60 + 6
= 240 + 6
= 246
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\(\hept{\begin{cases}\frac{3}{x}=-\frac{39}{81}\\\frac{y}{28}=-\frac{39}{81}\end{cases}\Leftrightarrow\hept{\begin{cases}x=-\frac{81}{13}\\y=-\frac{364}{27}\end{cases}}}\)
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1) x - 23 + x = x - 18
x + x - x = -18 + 23
x = 5
2) x - 17 - 31 = -15 - 28
x = -15 - 28 + 17 + 31
x = 5
3) 28 - 37 - 18 = x - 32 + 19
x = -32 + 19 - 28 + 37 + 18
x = 14
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\(a,\frac{7}{x}=\frac{x}{28}=>x\cdot x=28\cdot7=>x^2=196=>x^2=14^2\)\(=>x=14\)
\(b,\frac{10+x}{x+17}=\frac{3}{4}=>\left(10+x\right)\cdot4=\left(x+17\right)\cdot3=>40+x4=x3+51\)\(=>x4-x3=51-40=>x=11\)
( - 28 ) x ( -32 ) + 32 x ( 100 - 28 )
= 28 x 32 + 32 x 100 - 32 x 28
= 32 x ( 28 + 100 - 28 )
= 32 x 100
= 3200
(-28).(-32+32).(100-28)
=(-28).(-32)+32.100-28
=[(-28)-28].[(-32)+32].100
=(-56).0.100
=0