已知a+(1/a)=2,求:(1)a²+(1/a²)的值 (2)a³+(1/a³)的值 (3)a^4+(1/a^4)的值
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已知a+(1/a)=2,求:(1)a²+(1/a²)的值 (2)a³+(1/a³)的值 (3)a^4+(1/a^4)的值
已知a+(1/a)=2,求:(1)a²+(1/a²)的值 (2)a³+(1/a³)的值 (3)a^4+(1/a^4)的值
已知a+(1/a)=2,求:(1)a²+(1/a²)的值 (2)a³+(1/a³)的值 (3)a^4+(1/a^4)的值
(1)将 a+1/a=2 两边平方得 a^2+2+1/a^2=4 ,所以 a^2+1/a^2=2 .
(2)把 a+1/a=2 与 a^2+1/a^2=2 相乘,可得 a^3+1/a^3+a+1/a=4 ,
所以 a^3+1/a^3=4-(a+1/a)=4-2=2 .
(3)将 a^2+1/a^2=2 两边平方得 a^4+2+1/a^4=4 ,所以 a^4+1/a^4=2 .
a+1/a=2
﹙1﹚﹙a+1/a﹚²=2²
a²+2+1/a²=4
a²+1/a²=2
﹙2﹚a³+1/a³
=﹙a+1/a﹚﹙a²-1+1/a²﹚
=2×﹙2-1﹚
=2
﹙3﹚a^4+1/...
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a+1/a=2
﹙1﹚﹙a+1/a﹚²=2²
a²+2+1/a²=4
a²+1/a²=2
﹙2﹚a³+1/a³
=﹙a+1/a﹚﹙a²-1+1/a²﹚
=2×﹙2-1﹚
=2
﹙3﹚a^4+1/a^4
=﹙a²+1/a²﹚²-2
=2²-2
=2 .
收起
(1)a²+(1/a²)
=(a+1/a)^2-2
=2^2-2
=2
(2)a³+(1/a³)
=(a+1/a)^3-3a²(1/a)-3a(1/a^2)
=2^3-3(a+1/a)
=8-3*2
=2
(3)a^4+(1/a^4)
=(a^2+1/a^2)^2-2
=2^2-2
=2