# x＋x½＝1，不使用赋值法，如何求x ## 求x加x分之一的值域

f(x) = x + 1/x

x->0+ , f(x)->∞

x->0-, f(x)->-∞

f'(x) = 1 - 1/x^2

f'(x) =0

x^2 -1 =0

x= 1 or -1

f''(x) = 2/x^3

f''(1) =2 >0 (min)

f''(-1) =-2<0 (max)

max f(x) = f(-1) = -1 + 1/(-1) = -2

min f(x) =f(1) = 1 + 1/1 =2

## xln(1+x²)的原函数是什么

f  xln(1+x²)dx = 1/2 f ln(1+x²) dx²   =1/2 f  ln(1+x²)d(1+x²)

f lnx dx= xlnx- f  xd(lnx) =xlnx -f dx= x(lnx-1)

## x²+x+1=0怎么做

1、当Δ>0时，方程ax^2＋bx＋c＝0(a≠0)有两个不等的实数根；

2、当Δ＝0时，方程ax^2＋bx＋c＝0(a≠0)有两个相等的实数根；

3、当Δ<0时，方程ax^2＋bx＋c＝0(a≠0)无实数根。

1、二次项系数化为1

2、移项，左边为二次项和一次项，右边为常数项。

3、配方，两边都加上一次项系数一半的平方，化成（x=a)^2=b的形式。

4、利用直接开平方法求出方程的解。

## x的平方+x=1 怎么解？

x的平方+x=1

x的平方+x-1 =0

x的平方+x+1/4-1/4-1 =0

(x+1/2)的平方-5/4=0

(x+1/2-√5/2)(x+1/2+√5/2)=0

x=-1/2+√5/2或x=-1/2-√5/2
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