X乘X减2.5X=6,  求X!

问题描述:

X乘X减2.5X=6,  求X!

x^2-2.5x=6
x^2-2.5x-6=0
(x^2-2.5x+25/16)-25/16-6=0
(x-5/4)^2-121/16=0
(x-5/4+11/4)(x-5/4-11/4)=0
(x+5/2)(x-4)=0
x=-2.5,x=4