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a) \(27+86-\left(29-5+84\right)\)
\(=27+86-29+5-84\)
\(=2+5-2\)
=5
b) \(39-\left(298-89\right)+299\)
\(=39-298+89+299\)
\(=129\)
a, \(A=\frac{2n+5}{n-1}=\frac{2n-2+7}{n-1}=\frac{2\left(n-1\right)+7}{n-1}=\frac{2\left(n-1\right)}{n-1}+\frac{7}{n-1}=2+\frac{7}{n-1}\)
Để A nguyên <=> n - 1 thuộc Ư(7) = {1;-1;7;-7}
| n-1 | 1 | -1 | 7 | -7 |
| n | 2 | 0 | 8 | -6 |
Vậy...
b, Gọi d là UCLN(30n+27,15n+13)
Ta có: 30n + 27 chia hết cho d
15n + 13 chia hết cho d => 2(15n+13) chia hết cho d => 30n+26 chia hết cho d
=> 30n+27 - (30n+26) chia hết cho d
=> 30n+27 - 30n-26 chia hết cho d
=> 1 chia hết cho d => d = {1;-1}
Vậy \(\frac{30n+27}{15n+13}\)tối giản
Đáp án là A
Ta có: 27.(-13) + 27.(-27) + (-14).(-27) = 27.(-13) + 27.(-27) + 14.27 = 27.[(-13) + (-27)+14] = 27[(-40) + 14] = 27.(-26) = -702)
2,
a) \(315-\left(135-x\right)=215\)
\(\Rightarrow135-x=315-215\)
\(\Rightarrow135-x=100\)
\(\Rightarrow x=135-100\)
\(\Rightarrow x=35\)
b) \(x-320:32=25\cdot16\)
\(\Rightarrow x-10=5^2\cdot4^2\)
\(\Rightarrow x-10=20^2\)
\(\Rightarrow x-10=400\)
\(\Rightarrow x=410\)
c) \(3\cdot x-2018:2=23\)
\(=3\cdot x-1009=23\)
\(\Rightarrow3\cdot x=1032\)
\(\Rightarrow x=1032:3\)
\(\Rightarrow x=344\)
d) \(280-9\cdot x-x=80\)
\(\Rightarrow280-x\cdot\left(9+1\right)=80\)
\(\Rightarrow280-10\cdot x=80\)
\(\Rightarrow10\cdot x=280-80\)
\(\Rightarrow10\cdot x=200\)
\(\Rightarrow x=20\)
e) \(38\cdot x-12\cdot x-x\cdot16=40\)
\(\Rightarrow x\cdot\left(38-12-16\right)=40\)
\(\Rightarrow x\cdot10=40\)
\(\Rightarrow x=40:10\)
\(\Rightarrow x=4\)
Ta có: A\(=\dfrac{1}{9}.\dfrac{1}{10}+\dfrac{1}{10}.\dfrac{1}{11}+\dfrac{1}{11}.\dfrac{1}{12}+\dfrac{1}{12}.\dfrac{1}{13}+\dfrac{1}{13}.\dfrac{1}{14}+\dfrac{1}{14}.\dfrac{1}{15}\)
\(=\dfrac{1}{9}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{14}+\dfrac{1}{14}-\dfrac{1}{15}\)
\(=\dfrac{1}{9}-\dfrac{1}{15}=\dfrac{2}{45}\)
\(A=\dfrac{1}{9}.\dfrac{1}{10}+\dfrac{1}{10}.\dfrac{1}{11}+\dfrac{1}{11}.\dfrac{1}{12}+\dfrac{1}{12}.\dfrac{1}{13}+\dfrac{1}{13}.\dfrac{1}{14}+\dfrac{1}{14}.\dfrac{1}{15}\)
\(=\dfrac{1}{9}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{14}+\dfrac{1}{14}-\dfrac{1}{15}\)
\(=\dfrac{1}{9}-\dfrac{1}{15}\)
\(=\dfrac{2}{45}\)
-Chúc bạn học tốt-
|(5/8-5/14)+(3/8-9/14)|:4/7
=|(5/8+3/8)+(-5/14-9/14)|:4/7
=|1+(-1)|:4/7
=0
a) \(A=\left(-13\right)+\left(-27\right)+\left(-65\right)\)
\(=-105\)
b) \(B=\left(-9\right)+\left(-14\right)+27\)
\(=4\)