(39又2分之1)²-(10又2分之1)²简便计算

问题描述:

(39又2分之1)²-(10又2分之1)²简便计算

(39又2分之1)²-(10又2分之1)²
=(40-0.5)²-(10+0.5)²
=(40-0.5+10+0.5)×(40-0.5-10-0.5)
=50×29
=1450