maths problem 02

3)logx + log y = 2log (xy) = 2xy = 1001/x + 1/y >= 2√ [1/(xy)] = 2√(1/100) = 1/5 , 當 1/x = 1/y 時等號成立。最小值是_1/5_, 此時x = 10__; y = 10__.4)y = 1/(x-3) + xy - 3 = (x-3) + 1/(x-3) >= 2√[(x-3)(1/(x-3))] = 2 當 x-3 = 1/(x-3)
即 x = 4 時等號成立。
最_小_值是_2_; 此時x = _4_.

2010-09-29 19:16:29 補充：
Corr :

最_小_值是_2+3 = 5_; 此時x = _4_.

2010-09-29 19:57:45 補充：
x-3 = 1/(x-3)

x = 2 or 4 ,

因 x > 3 , 捨去x = 2