解答：$ecause(frac{sqrt{5}}{2}x^2+frac{1}{2sqrt{5}}y^2)+(frac{2}{sqrt{5}}y^2+frac{sqrt{5}}{2}z^2)ge xy+2yz herefore $最大值为$frac{sqrt{5}}{2}$
解答：$ecause(frac{sqrt{5}}{2}x^2+frac{1}{2sqrt{5}}y^2)+(frac{2}{sqrt{5}}y^2+frac{sqrt{5}}{2}z^2)ge xy+2yz herefore $最大值为$frac{sqrt{5}}{2}$