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x2+(a+b)x+ab=(x+a)(x+b)
此类多项式x2+(a+b)x+ab的特征是二次项系数为1,常数项为两数之积,一次项系数为这两数之和.
猜想并填空:x2+8x+15=x2+[()+()]x+()×()=(x+)(x+)
① x2+8x+12 ② x2-x-12
①x2-1=(x-1)(x+1);
②x3﹣1
=x3﹣x+x﹣1
=x(x2﹣1)+x﹣1
=x(x﹣1)(x+1)+(x﹣1)
=(x﹣1)[x(x+1)+1]
=(x﹣1)(x2+x+1);
③x4﹣1
=x4﹣x+x﹣1
=x(x3﹣1)+x﹣1
=x(x﹣1)(x2+x+1)+(x﹣1)
=(x﹣1)[x(x2+x+1)+1]
=(x﹣1)(x3+x2+x+1);
…
45+44+43+42+4+1
= ×(4﹣1)(45+44+43+42+4+1)
= ×(46﹣1)
= .
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