最值问题是初等数学中经常碰到的一类问题 .有些最值问题用常规代数方法较难入手 ,但若把问题适当变形 ,揭示其相应的几何意义 ,问题实质就直观清楚 ,易于解决 .例 1　已知ｘ2 +2ｙ2 =1 ,求ｚ =ｘ2 + ｙ2 -4ｘ + 4最值 .解　由条件知ｘ2+ 2 ｙ2 =1是中心在原点 ,长轴在ｘ轴上的 The problem of the most value is a type of problem that is often encountered in elementary mathematics. Some of the most value problems are more difficult to solve with conventional algebraic methods. However, if the problem is appropriately deformed to reveal its corresponding geometric meaning, the problem is intuitionally clear and easy to solve. Example 1 Known x2 +2y2 =1, find z =x2 + y2 -4x + 4 the most value. Solution by the condition known x2+2 y2 =1 is the center at the origin, the long axis on the x-axis