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Gấp quá em nhỉ!
A = 2 + 22 + 23 +24 + 25 +....+2200
2A = 22 + 23 + 24 + 25+....+2200 + 2201
2A - A = 2201 - 2
A = 2201 - 2
A = (24)50.2 - 2
A = (\(\overline{...6}\))50.2 - 2
A = \(\overline{...6}\) . 2 - 2
A = \(\overline{...2}\) - 2
A = \(\overline{...0}\) \(\Rightarrow\) A = C . 10 ( C \(\in\) N*)
Thay A = C .10 vào biểu thức B = -1,9 . A ta có :
B = -1,9 . C .10
B = -(1,9 .10) .C
B = - 19.C vì C \(\in\) N \(\Rightarrow\) B \(\in\) Z (đpcm)
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a) (23.37-11.37):37
=(23-11).37:37
=12.(37:37)
=12.1
=12
b)91.172+91.13-91.85
=91.(172+13-85)
=91.100
=9100
a, ( 23 × 37 - 11 × 37 ) ÷ 37
= 37 × ( 23 - 11 ) ÷ 37
= 37 × 12 ÷ 37
= 444 ÷ 37
= 12
b, 91 × 172 + 91 × 13 - 91 × 85
= 91 × ( 172 + 13 - 85 )
= 91 × 100
= 91000
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Bài 10:
$-A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}$
$=\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{9.10}$
$=\frac{5-4}{4.5}+\frac{6-5}{5.6}+\frac{7-6}{6.7}+...+\frac{10-9}{9.10}$
$=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+....+\frac{1}{9}-\frac{1}{10}$
$=\frac{1}{4}-\frac{1}{10}=\frac{3}{20}$
$\Rightarrow A=\frac{-3}{20}$
Bài 11:
$A=\frac{2n}{n+3}=\frac{2(n+3)-6}{n+3}=2-\frac{6}{n+3}$
Để $A$ nguyên thì $\frac{6}{n+3}$ nguyên.
Với $n$ nguyên thì điều trên xảy ra khi $6\vdots n+3$
$\Rightarrow n+3\in\left\{\pm 1; \pm 2; \pm 3; \pm 6\right\}$
$\Rightarrow n\in\left\{-4; -2; -1; -5; -6; 0; -9; 3\right\}$
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6^31=186
3^23=69
2020^3010=6080200
Mik ko chắc nx.Số to quá mik ko lm đầy đủ đc nên mik viết luôn kết quả nha,có j cho mik xl
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c.
\(5^3.73-5^3.36-37.25\)
\(=5^3\left(73-36\right)-37.5^2\)
\(=5^3.37-37.5^2\)
\(=5^2.37\left(5-1\right)\)
\(=5^2.37.4=100.37=3700\)
d.
\(45+15.13-3.2^4=15\left(3+13\right)-3.16\)
\(=15.16-3.16=16.\left(15-3\right)=16.12=192\)
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\(2\cdot\left(x-1\right)+3\cdot\left(x-2\right)=0\\ \Rightarrow2x-2+3x-6=0\\ \Rightarrow5x-8=0\\ \Rightarrow5x=0+8\\ \Rightarrow5x=8\\ \Rightarrow x=\dfrac{8}{5}\)
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1: Để C là số nguyên thì 2n+2-3 chia hết cho n+1
=>\(n+1\in\left\{1;-1;3;-3\right\}\)
=>\(n\in\left\{0;-2;2;-4\right\}\)
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\(37-2.\left(x+1\right)=15\)
\(2.\left(x+1\right)=37-15\)
\(2.\left(x+1\right)=22\)
\(x+1=22:2\)
\(x+1=11\)
\(x=11-1\)
\(x=10\)
-2 ( x + 1 ) = 37 - 15
-2 ( x + 1) = 22
x + 1 = -11
x = -12
bài 1 a bài 3 mũ 4 b 5 c 25 mũ 3
dễ thôi mà,chịu thua T_T