设函数f(x)=x−3,(x≥10)f(f(x+5)),(x<10),则f(5)=_.

问题描述:

设函数f(x)=

x−3,(x≥10)
f(f(x+5)),(x<10)
,则f(5)=______.

∵5<10,∴f(5)=f(f(5+5))=f(f(10))=f(7)
∵7<10,∴f(7)=f(f(7+5))=f(f(12))=f(9)
f(9)=f(f(9+5))=f(f(14))=f(11)=11-3=8
故答案为:8