今日知识点：Quadratic functions
Rules of indices
A quadratic function is a function ax2 + bx + c, where a, b and c are constants and the
highest power of x is 2.
The numbers a and b are called the coefficients of x2 and x, and c is the constant term.
Completing the square.
- a) The coefficient of x2 must be +1.
- b) Halve the coefficient of x, square it then add it and subtract it.
例题：
小试牛刀：
Complete the square in –3x2 – 24x + 5.
答案解析: