From the window we can see the blue sky and green trees .and it is good for our eyes.中文
问题描述：
From the window we can see the blue sky and green trees .and it is good for our eyes.中文
答
从窗户那我们可看到蓝天绿树,而这有助于保眼已知：a=x的平方-2x-1，b=2x的平方-6x+3，求3a-【（2a-b）-2（a-b）】的值，其中x等于-717