已知实数a满足a2-a-1=0,求a8+7a-4的值
来源:学生作业帮 编辑:搜狗做题网作业帮 分类:数学作业 时间:2024/08/12 14:07:43
已知实数a满足a2-a-1=0,求a8+7a-4的值
2 8 -4 为次方
2 8 -4 为次方
![已知实数a满足a2-a-1=0,求a8+7a-4的值](/uploads/image/z/15016551-15-1.jpg?t=%E5%B7%B2%E7%9F%A5%E5%AE%9E%E6%95%B0a%E6%BB%A1%E8%B6%B3a2-a-1%3D0%2C%E6%B1%82a8%2B7a-4%E7%9A%84%E5%80%BC)
由a^2-a-1=0得,a^2=a+1,
于是a^4=(a+1)^2=a^2+2a+1=3a+2
a^8=(3a+2)^2=9a^2+12a+4=21a+13
a^8+7a^-4=21a+13+7/(3a+2)
=(63a^2+81a+26+7)/(3a+2)
=(63a+63+81a+33)/(3a+2)
=(144a+96)/(3a+2)=48
2.
a^2-a-1=0
a^2=a+1
a^8+7a^-4
=a^6*a^2+7a^2-4
=a^6(a+1)+7a^2-4
=a^7+a^6+7a^-4
=a^5(a+1)+a^6+7a^2-4
=2a^6+a^5+7a^-4
=3a^5+2a^4+7a^-4
=5a^4+3a^3+7a^-4
=8a^3+5a^2+7a^-4
=13a^2+8a+7a^-4
=21a+13+7a^-4
=34+21a^-1+7a^-4
=34+21a^-1+7a^-2-7a^-3
=34+14a^-1+14a^-2
=48
于是a^4=(a+1)^2=a^2+2a+1=3a+2
a^8=(3a+2)^2=9a^2+12a+4=21a+13
a^8+7a^-4=21a+13+7/(3a+2)
=(63a^2+81a+26+7)/(3a+2)
=(63a+63+81a+33)/(3a+2)
=(144a+96)/(3a+2)=48
2.
a^2-a-1=0
a^2=a+1
a^8+7a^-4
=a^6*a^2+7a^2-4
=a^6(a+1)+7a^2-4
=a^7+a^6+7a^-4
=a^5(a+1)+a^6+7a^2-4
=2a^6+a^5+7a^-4
=3a^5+2a^4+7a^-4
=5a^4+3a^3+7a^-4
=8a^3+5a^2+7a^-4
=13a^2+8a+7a^-4
=21a+13+7a^-4
=34+21a^-1+7a^-4
=34+21a^-1+7a^-2-7a^-3
=34+14a^-1+14a^-2
=48
已知实数a满足a2-a-1=0,求a8+7a-4的值
已知满足等式a2次-a-1=0,求代数式a8次+7a负4次的值
已知实数a满足a2+2a-1=0求(1 /a+1)-(a+3/a2-1)*(a2-2a+1/a2+4a+3)的值
已知a2+a+1=0,求1+a+a2+…+a8的值.
已知实数a满足a2+2a-15=0,求1a+1
已知实数a,b满足 a2+b2=ab+a+b-1,求a+b的值.
已知实数a、b满足a2-2a=1,b2-2b=1 ,求 的值.
已知实数a、b满足(a-3)2+|2a-3b+7|=0,求代数式a2-b2的值.
已知实数 满足:a2-2a-5=0,5b2+2b-1=0,求a2+1/b2的值
已知实数a、b满足a2+b2+a2b2=4ab-1,则a+b的值为______.
已知实数a.b满足a2+3a+1=0.b2+3b+1=0.求a/b+b/a的值
已知实数a满足绝对值a-1+根号a-2=a,求a的值