(1)计算:|-5|-(
2
(2)化简:(a+2b)(a−2b)−
(3)先化简,再求值:2b2+(a+b)(a-b)-(a-b)2,其中a=-3,b=
(4)因式分解:6xy2-9x2y-y3.
(5)因式分解:4+12(x-y)+9(x-y)2.
(6)因式分解:a4-16.
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