有很多三角函数的值域(最值)问题,利用单纯的三角知识难以解出,可考虑借助二次曲线,把函数的值域(最值)问题转化为直线的斜率或截距的范围问题,结合几何图形解答,简单直观.下面举例说明.1可借助圆(或椭圆)来求的函数例1(2005年全国高考题)当0xπ2时,函数f(x)=1+cos2x+8sin2xs There are many problems in the range of the trigonometric function (most value), which can hardly be solved by using simple trigonometric knowledge. It is considered to convert the value range (most value) of the function into the range of the slope or intercept of the straight line by means of the quadratic curve , Combined with the geometric solution to answer, simple and intuitive. The following examples .1 can be obtained by means of a circle (or ellipse) Example 1 (2005 National Entrance Examination) When 0xπ2, the function f (x) = 1 + cos2x + 8sin2xs