Question

一道初中数学题！！求救啊！！在线等！！～～急急急急急急急急急急急急急急急急！！！！！！！！！

已知a=(2√2+√5)/(√5-√2),求代数式
a^5-7^2+6a^3-7a^2+11a+13

Answer 1

a=(2√2+√5)/(√5-√2)
=(2√2+√5)(√5+√2),/(√5-√2)(√5+√2)
=(3√10+9)/3
=√10+3
所以a-3=√10
两边平方
a^2-6a+9=10
a^2-6a=1

a^5-7(a^4)+6(a^3)-7(a^2)+11a+13
=a^5-6a^4-a^4+6(a^3)-7(a^2)+11a+13
=a^3(a^2-6a)-a^4+6(a^3)-7(a^2)+11a+13
=a^3-a^4+6(a^3)-7(a^2)+11a+13
=-a^4+7a^3-7(a^2)+11a+13
=-a^4+6a^3+a^3-7(a^2)+11a+13
=-a^2(a^2-6a)+a^3-7(a^2)+11a+13
=-a^2+a^3-7(a^2)+11a+13
=a^3-6a^2-2a^2+11a+13
=a(a^2-6a)-2a^2+11a+13
=a-2a^2+11a+13
=-2a^2+12a+13
=-2(a^2-6a)+13
=-2+13
=11

Answer 2

把题目写好一点，看不通

Answer 3

不会