已知X＜5/4 求函数y=4x-2+1/(4x-5)的最大值.

题目

已知X＜5/4 求函数y=4x-2+1/(4x-5)的最大值.
已知x＞0 y＞0 且1/x + 9/y =1 求x+y的最小值

答案

1)x＜5/4 ===>5-4x>0y=4x-2+1/(4x-5)=4x-5+1/(4x-5)+3=-[5-4x+1/(5-4x)]+35-4x+1/(5-4x)>=2√(5-4x)*1/(5-4x2)=2 (当且仅当5-4x=1/(5-4x）取到等号）ymax=-2+3=12)x+y=(x+y)*(1/x + 9/y)=1+9+9x/y+y/x=10+9x/y+y/x>=...