Question

这道数学题怎么做呢

Answer 1

追问

a+1=8怎么来的呢

追答

Answer 2

f(x)

=log<2>(x+1)                   ; x>3

=2^(x-3) +1                     ; x≤3

f(a)=3

To find  : f(a-5)

case 1:   a>3

f(a)= 3

log<2>(a+1)= 3

a+1 = 8

a=7  >3)

a-5 = 2 ≤3

f(a-5)= f(2) = 2^(2-3) +1   = 3

case 2: a≤3

f(a) = 3

2^(a-3) +1   =3

2^(a-3)=2

a-3 =1

a=4 

case 2: 舍去

ie

f(a)=3

f(a-5)=f(2)=3

追问

a+1=8怎么来的呢

追答

case 1: a>3
f(a)= 3
log(a+1)= 3
a+1 =2^3
a+1 = 8
a=7 >3)
a-5 = 2 ≤3
f(a-5)= f(2) = 2^(2-3) +1 = 3