Question

二次函数一般式怎么变成顶点式的?

Answer 1

y=ax^2+bx+c

=a(x^2+bx/a)+c

=a(x^2+bx/a+b^2/4a^2-b^2/4a^2)+c

=a(x^2+bx/a+b^2/4a^2)-b^2/4a+c

=a(x+b/2a)^2+(4ac-b^2)/4a

关键是对x^2+bx/a的配方