一个正方形的边长增加3cm,面积增加39cm2,求这个正方形的边长。
解:设这个正方形边长xcm,则
(x +3)2-x2=39,
解得x=5
答:这个正方形的边长是5cm
If he ________ busy now, he would have much more time to do exercise.
[ ]
A. doesn't
B. isn't
C. weren't
D. won't be
下列操作行为正确的是()
A.吹灭酒精灯;
B.钠倒入水槽着火,立即用水浇灭;
C.温度计也可以用来搅拌;
D.蒸馏时,用锥形瓶作蒸馏瓶