1、下列分解因式，正确的是（ ）.
A、\( – a + {a^3} = – a\left( {1 + {a^2}} \right)\)
B、\(2a – 4b + 2 = 2\left( {a – 2b} \right)\)
C、\({a^2} – 4 = {\left( {a – 2} \right)^2}\)
D、\( – {a^2} + 2a – 1 = – {\left( {a – 1} \right)^2}\)
2、如果\({x^2} + ax – 25 = \left( {x + 5} \right)\left( {x – 5} \right)\)，那么\(a = \) .
3、多项式\(3x{y^2}z – 6xy{z^2} – 12{x^2}y{z^2}\)中各项的公因式是 .
4、若多项式\({x^2} – 6x + b\)可变形为\({\left( {x – a} \right)^2} – 1\)，则\(b – a\)的值等于 .
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