\(f\left(x\right)=2x^3-3x^2+x+A\)

Để \(f\left(x\right)\)chia hết cho \(x+2\)thì \(f\left(-2\right)=0\)

\(\Rightarrow2.\left(-2\right)^3-3.\left(-2\right)^2+\left(-2\right)+A=0\)

\(\Leftrightarrow A=30\)

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TL

x=-1

HT 

\(\left(x+y\right)^2+3\left(x+y\right)-10\)

\(=\left(x+y\right)^2+5\left(x+y\right)-2\left(x+y\right)-10\)

\(=\left(x+y\right)\left(x+y+5\right)-2\left(x+y+5\right)\)

\(=\left(x+y-2\right)\left(x+y+5\right)\)

\(\left(2m-a\right)^2+\left(2m-b\right)^2+\left(2m-c\right)^2+\left(2m-d\right)^2+\left(2m-e\right)^2\)

\(=4m^2-4ma+a^2+4m^2-4mb+b^2+4m^2-4mc+c^2+4m^2-4md+d^2+4m^2-4me+e^2\)

\(=20m^2-4m\left(a+b+c+d+e\right)+a^2+b^2+c^2+d^2+e^2\)

\(=20m^2-4m.5m+a^2+b^2+c^2+d^2+e^2\)

\(=a^2+b^2+c^2+d^2+e^2\)

a) 

\(\left(x+1\right)^2+x\left(2-x\right)\)

\(=x^2+2x+1+2x-x^2\)

\(=4x+1\)

b) 

\(\left(x-2\right)^3-\left(x-2\right)\left(x^2+2x+4\right)\)

\(=x^3-6x^2+12x-8-x^2+8\)

\(=-6x^2+12x\)