L=-200x^2+4800x+3200x-76800
=-200(x^2-40x)-76800
=-200(x^2-40x+400)-76800+200*400
=-200(x-20)^2+3200
这个算式怎么化成下面这一个要详细过程,最好写在纸上拍下来给我.
L=-200x^2+4800x+3200x-76800
=-200(x^2-40x)-76800
=-200(x^2-40x+400)-76800+200*400
=-200(x-20)^2+3200