用sas做回归分析;

proc reg data=engine graphics;

model power=speed;

plot power*speed/conf95 pred95;

symbol v=star;

run;

以上是可以画出散点图和置信区间图的，下面怎么就不可以了？

 data engine2;

set engine;

speedsq=speed**2;

run;

proc reg data=engine2 graphics;

model power=speed speedsq;

plot power*speed/conf95 pred95;

symbol v=star;

这里的graphics怎么用？