类型一 :二次根式的意义例 1　 x是怎样的实数时 ,下列各式在实数范围内有意义 ?(1) 2 x- 3;　　 (2 ) x2 - 2 x + 1;(3) 7- 3x;　　 (4) x2 - 2 x + 2。简析 :对于二次根式 a ,只有当被开方数 a上非负数时 ,a才有意义 ;否则 ,如果被开方数是负数 ,二次根式 a没有意义。若被开 Type 1: Meaning of the Quadratic Roots Example 1 When x is a real number, the following formulas are meaningful in the real number range: (1) 2 x- 3; (2) x2 - 2 x + 1; (3) 7- 3x; (4) x2 - 2 x + 2 Analysis: For the secondary root a, only when the squared number a is non-negative, a is significant; otherwise, if the squared number is negative, the quadratic root a has no meaning. If opened