5.已知函数f(x)的定义域为(-∞,0)∪(0,+∞),图象关于原点对称,且当x<0时,xf′(x)<2f(x)恒成立,则f(1)、-$\frac{f(-4)}{16}$、$\frac{f(\sqrt{231})}{231}$的大小关系是( )
A. | $\frac{f(\sqrt{231})}{231}$<-$\frac{f(-4)}{16}$<f(1) | B. | f(1)<-$\frac{f(-4)}{16}$<$\frac{f(\sqrt{231})}{231}$ | ||
C. | -$\frac{f(-4)}{16}$<$\frac{f(\sqrt{231})}{231}$<f(1) | D. | $\frac{f(\sqrt{231})}{231}$<f(1)<-$\frac{f(-4)}{16}$ |
3.若平面α的斜线l在α上的射影为l′,直线b∥α且b⊥l′,则b与l( )
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A. | 必相交 | B. | 必为异面直线 | C. | 垂直 | D. | 无法确定 |