解f(10)
=f(2*5)
=2f(5)
=2f(2*2.5)
=2*2f(2.5)
=2*2f(2*1.25)
=2*2*2f(1.25)
=8f(1.25)
=8*1.25^2
=8*5/4*5/4
=25/2
=12.5