1-385=3854=-485-3-2885=385]36
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![](https://rs.olm.vn/images/avt/0.png?1311)
385 x 485 + 386 x 515
= 385 x ( 485 + 515 )
= 385 x 1000
= 385000
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
= 385 x 43 + [ 385 x ( 1 + 46 ) ]
= 385 x 43 + 385 x 47
= 385 x ( 43 + 47 )
= 385 x 90 = 34650
kb với mình đi
385 * 43 + ( 385 * 1 + 385 * 46 )=
=385 * ( 43 +46 +1 )
= 385 * 90
=34650
![](https://rs.olm.vn/images/avt/0.png?1311)
a) (-385 + 210) + (385 - 217)
= -385 + 210 + 385 - 217
= (-385 + 385) + (210 – 217)
= 0 + (-7) = -7
b) (72 - 1 956) - (-1 956 + 28)
= 72 - 1 956 + 1956 - 28
= ( 1956 – 1956) + ( 72 – 28)
= 0 + 44 = 44.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
( x - 1 ) ( x + 9 ) ( x + 5 ) ( x + 3 ) = 385
⇔ ( x2 + 8x - 9 ) ( x2 + 8x + 15 ) = 385
Đặt t = x2 + 8x - 9, ta có :
t ( t + 24 ) = 385
⇔ t2 + 24t + 144 = 529
⇔ ( t + 12 )2 = 232
⇔ t = 11
⇒ x2 + 8x - 9 = 11
⇔ x2 + 8x - 20 = 0
⇔ ( x - 2 ) ( x + 10 ) = 0
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x+10=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-10\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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1. 385 x 385+ 385 x 615 = 385 ( 385 + 615)
= 385 x 1000
= 385000
2a) 6 x (X + 7545) = 28542 x6
6X + 45270 = 171252
6X = 125982
x= 125982:6
x= 20997
b) (X : 4) x8 = 9 x 8
( X :4 ) x 8 = 72
X : 4 = 72 :8
X : 4 = 9
x = 9 x 4
X= 36\(\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=-385\cdot149+385\cdot298-298\cdot149-298\cdot385-683\cdot851\)
\(=-683\cdot149-683\cdot851=-683000\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x+2x+3x+...+9x+10x=385\)
\(x.\left(1+2+3+...+10\right)=385\)
\(55x=385\)
\(x=\frac{385}{55}\)
\(x=7\)
Vậy \(x=7\)
Tham khảo nhé~
x.1 + x.2 + x.3 + ... + x.9 + x.10 = 385
x. ( 1 + 2 + 4 + 5 + 6 + 7 + 8 + 9 + 10 ) = 385
x. 55 = 385
x = 385 : 55
x = 7
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