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

\(\Leftrightarrow-x^2+2x-1=0\)

\(\Leftrightarrow x^2-2x+1=0\)

\(\Leftrightarrow\left(x-1\right)^2=0\)

\(\Leftrightarrow x-1=0\)

\(\Leftrightarrow x=1\)

\(7dm8mm=0,708m\)

d, \(x^4-2x^3+2x-1\)

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

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

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

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

\(=\left(x-1\right)^3\times\left(x+1\right)\)

e, \(x^3-2x^2-5x+6\)

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

\(=x^2\times\left(x-1\right)-x\times\left(x-1\right)-6\left(x-1\right)\)

\(=\left(x-1\right)\times\left(x^2-x-6\right)\)

\(=\left(x-1\right)\times\left(x^2+2x-3x-6\right)\)

\(=\left(x-1\right)\times\left(x\times\left(x+2\right)-3\left(x+2\right)\right)\)

\(=\left(x-1\right)\times\left(x+2\right)\times\left(x-3\right)\)

Phan Quỳnh Hoa :

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

\(=\left(2x\right)^2-2\times2x\times3y+\left(3y\right)^2\)

\(=4x^2-12xy+9y^2\)

\(\left(x-\dfrac{1}{2}\right)^2\)

\(=x^2-2x\times\dfrac{1}{2}+\left(\dfrac{1}{2}\right)^2\)

\(=x^2-x+\dfrac{1}{4}\)