已知函數(shù)f(x)=x2+1,x>0,1 xf(2x)的x的取值范圍是?
已知函數(shù)f(x)=x2+1,x>0,1 x<0,則滿足不等式f(1-x2)>f(2x)的x的取值范圍是?
優(yōu)質(zhì)解答
答:
x>0,f(x)=x^2+1>1,f(x)是增函數(shù)
x<0,f(x)=1
f(1-x^2)>f(2x)
1)當(dāng)1-x^2>0并且2x<0即-1f(1-x^2)=(1-x^2)^2+1>1
f(2x)=12)當(dāng)1-x^2>0并且2x>=0即0=f(1-x^2)>f(2x)>f(0)=1
1-x^2>2x
x^2+2x+1<2
-1-√2所以:0<=x<√2-1
3)當(dāng)1-x^2<0時,f(1-x^2)取得最小值1,不存在f(1-x^2)>f(2x)
綜上所述:-1