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24 . 25 + ( 4 . 6 ) . 37 + 24 . 38
24 . 25 + 24 . 37 + 24 . 38
24 . ( 25 + 37 + 38 )
24 . 100
2400
24 . 25 + 4 . 37 . 6 +24 . 38
= 24 . 25 + 24 . 37 + 24 . 38
= 24 . ( 25 + 38 + 37 )
= 24 . 100 = 2400
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a, =46x(-217+117) =46x(-100)=-4600
b, =-25x(78-28)=-25x50=-1250
c,=35(-63-23)=35x(-86)=3010
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a)\(A=\frac{1}{15}+\frac{1}{35}+...+\frac{1}{195}=\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{13.15}=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{15}\right)=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{15}\right)=\frac{2}{15}\)
b)\(M=1+3+3^2+...+3^{25}=\frac{3^{26}-1}{3-1}=\frac{3^{26}-1}{2}
![](https://rs.olm.vn/images/avt/0.png?1311)
Đặt \(A=\)\(\frac{1}{15}+\frac{1}{35}+...+\frac{1}{143}\)
\(=\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{11.13}\)
\(2A=\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{11.13}\)
\(2A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{13}\)
\(2A=\frac{1}{3}-\frac{1}{13}=\frac{10}{39}\)
\(A=\frac{5}{39}\)
Câu còn lại cx dựa như vậy nhé bn !
Chúc bn hc tốt <3
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a) 320 x 63 - 16 x 20 + 32 x 370
= 320 x 63 - 320 x + 320 x 37
= 320 x ( 63 - 1 + 37 )
= 320 x 99
= 320 x ( 100 - 1 )
= 320 x 100 - 320
= 32000 - 320 = 31 680
b) 35 x 61 + 215 x 5 + 35 x 39 + 57 x 25
= 5 x 427 + 5 x 215 + 5 x 273 + 5 x 285
= 5 x ( 427 + 215 + 273 + 285 )
= 5 x 1200 = 6000
c) 34 x 24 - 94 x 6 + 83 x 48 - 47 x 88
= 204 x 4 - 4 x 141 + 996 x 4 - 1034 x 4
= 4 x ( 204 - 141 + 996 - 1034 )
= 4 x 25 = 100
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\(35\cdot99+35+25\cdot63+25\cdot63+25\cdot38-25\)
\(=35\cdot\left(99+1\right)+25\cdot\left(63+63+38-1\right)\)
\(=35\cdot100+25\cdot163\)
\(=3500+4075\)
\(=7575\)
\(35\cdot99+35+25\cdot63+25\cdot63+25\cdot38-25\)
\(=35(99+1)+25(63+63+38-1)\)
\(=35\cdot100+25\cdot163\)
\(=3500+4075\)
\(=7575\)