一个长方形的长,宽,高分别是(x+1)cm,x(cm),(x+2)cm.若长,宽,高分别增加2cm,1cm,2cm,

增加的体积
=（x+1+2）×(x+1)×（x+2+2）-（x+1）×(x)×（x+2)
=(x+3)(x+1)(x+4)-x(x+1)(x+2)
=(x+1)[(x+3)(x+4)-x(x+2)]
=(x+1)[x²+7x+12-x²-2x]
=(x+1)(5x+12)
=5x²+17x+12