(-12)x7+(-8)x7+4x(-25)+(-6)x(-25)=(-12-8)x7+(-25)(4x-6x)=7x(-20)+(-25)(-2x)=-140x+50x=-90x

126-53+20-(53+126) = 126-53+20-179 = 73+20-179 = 93-179 = -86

\(A=2+2^2+...+2^{10}\)

\(A=\left(2+2^2\right)+...+\left(2^9+2^{10}\right)\)

\(A=2\left(1+2\right)+...+2^9\left(1+2\right)\)

\(A=2\cdot3+...+2^9\cdot3\)

\(A=3\cdot\left(2+...+2^9\right)⋮3\left(đpcm\right)\)

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chịu!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

\(A=2+2^2+2^3+...+2^{10}\)

\(A=\left(2+2^2\right)+...+\left(2^9+2^{10}\right)\)

\(A=2.\left(1+2\right)+...+2^9.\left(1+2\right)\)

\(A=2.3+...+2^9.3\)

\(A=3.\left(2+...+2^9\right)\)

\(\Rightarrow A⋮3\)

(2+2²) chia hết cho 3

(2³+2^{4) chia hết cho 3}

(2⁵+2⁶) chia hết cho 3

(2⁷+2⁸) chia hết cho 3

(2⁹+2¹⁰) chia hết cho 3

=> A = 2 + 2²+ 2³+...+2¹⁰ chia hết cho 3

\(32-2\left(x+1\right)=42\)

\(\Rightarrow32-2x-1=42\)

\(\Rightarrow31-2x=42\)

\(\Rightarrow2x=31-42\)

\(\Rightarrow2x=-11\)

\(\Rightarrow x=\frac{-11}{2}\)

\(\Rightarrow x=-5,5\)

32-2.(x+1)=42

=>2.(x+1)=32-42

=>2.(x+1)=-10

=>x+1=-10:2

=>x+1=-5

=>x=-5-1

=>x=-6

\(156-\left(x+61\right)=82\)

\(\left(x+61\right)=156-82\)

\(\left(x+61\right)=74\)

\(\Rightarrow x=13\)

PP/ss: Lm từng câu ạ ((:

\(156-\left(x+61\right)=82\)

\(\Rightarrow x+61=156-82\)

\(\Rightarrow x+61=74\)

\(\Rightarrow x=74-61\)

\(\Rightarrow x=13\)