墙原高为:
√(2.5^2-0.7^2)=2.4
设梯子底滑出x米,可得:
(2.4-0.4)^2+(0.7+x)^2=2.5^2
4+(0.7+x)^2=6.25
(0.7+x)^2=2.25
0.7+x=1.5
x=0.8