4、①21×3.14+62×3.14+17×3.14
=3.14×(21+62+17)
=3.14×100
=314
②758²-258²
=（758+258）(758-258)
=1016×500
=508000
5、①（a-b)²+4ab
=a²-2ab+b²+4ab
=a²+2ab+b²
=(a+b)²
②（p-4）（p+1)+3p
=p²-3p-4+3p
=p²-4
=(p+2)(p-2)
③4xy²-4x²y-y³
=-y(4x²-4xy+y²）
=-y（2x-y)²
④3ax²-3ay²
=3a（x²-y²)
=3a(x+y)(x-y)
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