(x+y)²≧2xy=24
当x>0.y>0时,x+y有最小值2根号6
当x过程能再详细点吗？(1)当x>0.y>0时,x+y>0(x+y)²≧24两端开方得x+y≧根号24=2根号6x+y有最小值2根号6(2)当x<0.y<0时,x+y<0(x+y)²≧24两端开方得x+y≦-根号24=-2根号6x+y有最大值-2根号6(3)5X²-10x-7=5(X-1)²-125(X-1)²≧0当x=1时,5(X-1)²-12=-125X²-10x-7有最小值-12