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b/ =-36.16+36.41-16.41+16.36
=36.41-16.41
=41.(36-16)
=41.20
=820
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Câu 1:
\(=\dfrac{21}{31}+\dfrac{1}{3}-\dfrac{44}{53}+\dfrac{10}{31}-\dfrac{9}{53}=\dfrac{1}{3}\)
Câu 2:
1: =>1,3x=-1,31
=>130x=-131
=>x=-131/130
2: =>(4,5-2x)=11/14:(-11/7)=-7/14=-1/2=-0,5
=>2x=5
=>x=5/2
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30 x 31 x 32 x.....................x 39 x 40 chia hết cho 7
111 chia hết cho 7
=> 30 x 31 x 32 x.....................x 39 x 40 + 111 chia hết cho 7
Ta có: 30x31x32x…x39x40+111
= 30x31x…x36x38x…x40x37+3x37
=(30x31x…x36x38x…x30+3)x37
Vậy 30x31x32x…x39x40+111 chia hết cho 37
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A = 4.5 + 5.6 + 6.7 + ... + 30.31
3A = 3.4.5 + 3.5.6 + 3.6.7 + ... + 3.30.31
= (6 - 3).4.5 + (7 - 4).5.6 + (8 - 5).6.7 + ... + (32 - 29).30.31
= 4.5.6 - 3.4.5 + 5.6.7 - 4.5.6 + 6.7.8 - 5.6.7 + ... + 30.31.32 - 29.30.31
= (4.5.6 + 5.6.7 + 6.7.8 + ... + 30.31.32) - (3.4.5 + 4.5.6 + 5.6.7 + ... + 29.30.31)
= 30.31.32 - 3.4.5 = 29760 - 60 = 29700
A = 29700 : 3 = 9900
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\(x+7=-12-3\)
\(x+7=-15\)
\(x=-15-7\)
\(x=-22\)
\(13-x=20-\left(-31\right)\)
\(13-x=51\)
\(x=13-51\)
\(x=-38\)
\(2x-41=-19-2\)
\(2x-41=-21\)
\(2x=-21+41\)
\(2x=20\)
\(x=20:2\)
\(x=10\)
\(\left(x-1\right).2+14=30-\left(-14\right)\)
\(2x-2+14=44\)
\(2x-2=44-14\)
\(2x-2=30\)
\(2x=30+2\)
\(2x=32\)
\(x=16\)
cho minh hoi:tap hop cac so co 2 chu so chia het cho va 9
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Ta có : \(E=25\cdot30+10\)
\(E=750+10\Rightarrow E=760\)
\(F=31\cdot26-10\)
\(F=806-10\Rightarrow F=796\)
Do 760 < 796 nên E < F hoặc \(E=25\cdot30+10< F=31\cdot26-10\)
![](https://rs.olm.vn/images/avt/0.png?1311)
`30x + 1335 = 31x`
`<=> 1335 =x`
Vậy `x = 1335`
\(\left(x.30\right)+1335=31.x\)
\(31.x-30.x=1335\)
\(x=1335\)