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\(a.\left(67-5759\right)+5759\\ =67-5759+5759\\ =67+\left(5759-5759\right)\\ =67+0\\ =67\)
\(b.\left(-3023\right)-\left(765-3023\right)\\ =-3023-765+3023\\ =\left(-3023+3023\right)-765\\ =0-765\\ =-765\)
\(c.631+\left[587-\left(287+231\right)\right]\\ =631+587-287-231\\ =\left(631-231\right)+\left(587-287\right)\\ =400+300\\ =700\)
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Đáp án cần chọn là: B
53 23 + − 30 23 ≤ x ≤ 1 5 + 1 6 + 79 30 1 ≤ x ≤ 3
x∈{1;2;3}
Vậy có tất cả 3 giá trị của x.
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sách Nâng cao phát triển lớp 6 tập 1
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A(135792468-123456789+350-1234)*2-30
A=12334795.2-30
A=24669590-30
A=24669560
B 765*13-(569-243):2
B=9945-326:2
B=9945-163
B=9782
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\(A=1+5^2+5^3+...+5^{2015}+5^{2016}\)
\(5A=5+5^3+5^4+...+5^{2016}+5^{2017}\)
\(4A=\left(5+5^3+5^4+...+5^{2016}+5^{2017}\right)-\left(1+5^2+5^3+...+5^{2015}+5^{2016}\right)\)
\(=5+5^{2017}-\left(1+5^2\right)\)
\(=4+5^{2017}-5^2\)
\(A=\frac{4+5^{2017}-5^2}{4}\)
Ta có : 5A = 5 + 5^3 + 5^4 + ... + 5^2016 + 5^2017
=> 5A - A = ( 5 + 5^3 + 5^4 + ... + 5^2016 + 5^2017 ) - ( 1 + 5^2 + 5^3 + ... + 5^2015 + 5^2016 )
=> 4A = 4 + 5^2 + 5^2017
=> A = ( 4 + 5^2 + 5^2017 )/4
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a: =-5/6-3/7=-35/42-18/42=-53/42
b: =2/5-4/9=18/45-20/45=-2/45
c: =-24/35
d: =2/3x-5/4=-10/12=-5/6
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a: \(\Leftrightarrow x=\dfrac{1}{9}+\dfrac{5}{7}=\dfrac{52}{63}\)
b: \(\Leftrightarrow x=\dfrac{1}{10}+\dfrac{1}{15}=\dfrac{1}{6}\)
c: \(\Leftrightarrow x=\dfrac{-3}{7}-\dfrac{4}{5}+\dfrac{2}{3}=-\dfrac{59}{105}\)
d: \(\Leftrightarrow x=\dfrac{-2}{15}+\dfrac{3}{10}=\dfrac{1}{6}\)
=-3023-765+3023=-765
-765