Pove：　-x^7 -3X + 3 = 0 only has one real root (只有一實數根）

Pove：　-x^7 -3X + 3 = 0 only has one real root
其實用不到判別式的﹐因為不是二次
answer
f'(x)
=-7x^6-3
<0 (because x^6>=0)
So f(x) is strictly decreasing
This means that f(x) will only touch the x-axis 0 or 1 time...(*)
Now f(0)=3>0 ; f(1)=-1-3+3=-1<0
By intermediate value theorem , there should exist one x such that f(x)=0
Combine with (*) We prove that -x^7 -3X + 3 = 0 only has one real root

用判別式 b 2次 - 4 ac 是否 =0


但你條式係米打錯左..??

-x^7 (７次方??) -3X + 3

2007-10-22 01:35:42 補充：
其實用判別式..將 a, b, c 代入 b^2-4ac...當然 a 是 X二 次前面個數...b 是X前面個數....c 是常數...代入之後...計算....如果答案=0....甘finish it la..because 判別式=0 means 只有一實數根..but i think ur equation has some mistake...so if u give the equation to me.again ..i can help u to check it..^^