直线斜率为-1,与其最近的点斜率也是-1
y = x² - 2ln根号x = x² - lnx
y' = 2x - 1/x = -1
2x² + x -1 =0
(2x - 1)(x+ 1) = 0
x = 1/2 (舍去x = -1 < 0)
P(1/2,1/4 + ln2)
最近距离d = |2 + 1 + 4ln2 +1}/√(16 + 16) = (1 + ln2)/√2