比较大小是高中数学中常见的题型,也是高考数学中常考常新的题目·这类问题涉及面广泛,往往与不等式有关,同时又可包罗多种函数背景·其解法既灵活多样又有章可循·1最基本的通法——作差法例1(2006年陕西卷·理10)已知f(x)=ax2+2ax+4(0a3),若x1x2,x1+x2=1-a,则()A·f(x1)f Comparing sizes is a common problem in high school mathematics. It is also a subject often used in college entrance examination mathematics. This type of problem involves a wide range of topics, often related to inequality, and can include a variety of functional backgrounds. Its solution is both flexible and diverse. The most basic method that can be followed is the difference law 1 (Shaanxi Volume 10, 2006). It is known that f(x)=ax2+2ax+4(0a3) if x1x2,x1+x2=1-a , then () A · f (x1) f