Since f(1) = 3 is given we will find solutions for n = 2, 3, 4, 5
f(2) = f( 2 - 1 ) -5
= f(1) -5
We have f(1) given to us which is f(1) = 3 so we can replace f(1) with 3
= 3 - 5
= -2
f(2) = -2
f(3) = f( 3 - 1 ) -5
= f(2) -5
replace f(2) with -2 because previously we got f(2) = -2
= -2 -5
= -7
f(3) = -7
f(4) = f( 4 - 1 ) -5
= f(3) -5
replace f(3) with -7 because previously we got f(3) =-7
= -7 -5
= -12
f(4) = -12
f(5) = f( 5 - 1 ) -5
= f(4) -5
replace f(4) with -12 because previously we got f(4) = -12
= -12 -5
= -17
f(5) = -17
etc...
Therefore,
f(1) = 3
f(2) = -2
f(3) = -7
f(4) = -12
f(5) = -17
etc...
