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= [-2 + 4] + [-6+8] + ... +[-18 + 20]
= 2 + 2 + ... + 2
= 10
(-2) + 4 + ( -6) + 8 + (-10) + 12 + (-14) + 16 + (-18) + 20
=[(-2) + 12] + [4+(-14)] + [(-6)+16] + [8+(-18)] + [(-10)+20]
= 10 + (-10) + 10 + (-10) + 10
=(10 +10 +10) + [(-10) + (-10)]
= 30 + (-20)
= 10
\(\left(x+2\right)-2=0\)
\(\Rightarrow x+2-2=0\)
\(\Rightarrow x=0\)
\(\left(x+3\right)+1=7\)
\(\Rightarrow x+3+1=7\)
\(\Rightarrow x+4=7\)
\(\Rightarrow x=3\)
\(\left(3x-4\right)+4=12\)
\(\Rightarrow3x-4+4=12\)
\(\Rightarrow3x=12\)
\(\Rightarrow x=4\)
\(\left(5x+4\right)-1=13\)
\(\Rightarrow5x+4-1=13\)
\(\Rightarrow5x+3=13\)
\(\Rightarrow5x=10\)
\(\Rightarrow x=2\)
\(\left(4x-8\right)-3=5\)
\(\Rightarrow4x-8-3=5\)
\(\Rightarrow4x-11=5\)
\(\Rightarrow4x=16\)
\(\Rightarrow x=4\)
\(8-\left(2x+4\right)=2\)
\(\Rightarrow8-2x-4=2\)
\(\Rightarrow4-2x=2\)
\(\Rightarrow2x=2\)
\(\Rightarrow x=1\)
\(7+\left(5x+2\right)=14\)
\(\Rightarrow7+5x+2=14\)
\(\Rightarrow9+5x=14\)
\(\Rightarrow5x=5\)
\(\Rightarrow x=1\)
\(5-\left(3x-11\right)=1\)
\(\Rightarrow5-3x+11=1\)
\(\Rightarrow16-3x=1\)
\(\Rightarrow3x=15\)
\(\Rightarrow x=5\)
\(\dfrac{-2}{9}\cdot\dfrac{7}{15}+\dfrac{-2}{9}\cdot\dfrac{8}{15}+\dfrac{2}{3^2}\)
\(=-\dfrac{2}{9}\left(\dfrac{7}{15}+\dfrac{8}{15}\right)+\dfrac{2}{9}\)
\(=\dfrac{-2}{9}+\dfrac{2}{9}\)
=0
=>Chọn C
ĐặtA = 2 + 5 + 11 + .. + 47 + 65
5 = 2 + 3
11 = 5 + 3.2
20 = 10 + 3.3
32 = 20 + 3.4
47 = 32 + 3.5
65 = 47 + 3 .6
=> A = 2 + (11 + 32 + 47) + 20 + (5 + 65) = 2 + 90 + 20 + 70 = 182
