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观察下列式子的因式分解做法: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(x
题目详情
观察下列式子的因式分解做法:
①x2-1=
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)
…
(1)模仿以上做法,尝试对x5-1进行因式分解;
(2)观察以上结果,猜想xn-1=___;(n为正整数,直接写结果,不用验证)
(3)根据以上结论,试求45+44+43+42+4+1的值.
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)
…
(1)模仿以上做法,尝试对x5-1进行因式分解;
(2)观察以上结果,猜想xn-1=___;(n为正整数,直接写结果,不用验证)
(3)根据以上结论,试求45+44+43+42+4+1的值.
▼优质解答
答案和解析
(1)x5-1
=x5-x+x-1
=x(x4-1)+x-1
=x(x-1)(x3+x2+x+1)+(x-1)
=(x-1)[x(x3+x2+x+1)+1]
=(x-1)(x4+x3+x2+x+1);
(2)xn-1=(x-1)(xn-1+xn-2+…+x2+x+1);
(3)45+44+43+42+4+1
=(4-1)(45+44+43+42+4+1)×
=(46-1)×
=
.
=x5-x+x-1
=x(x4-1)+x-1
=x(x-1)(x3+x2+x+1)+(x-1)
=(x-1)[x(x3+x2+x+1)+1]
=(x-1)(x4+x3+x2+x+1);
(2)xn-1=(x-1)(xn-1+xn-2+…+x2+x+1);
(3)45+44+43+42+4+1
=(4-1)(45+44+43+42+4+1)×
1 |
3 |
=(46-1)×
1 |
3 |
=
46-1 |
3 |
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