f(1) = 4 is given
f(n) = f(n-1)-4 is the recursive step or rule
f(2) = f(2-1)-4 ... replace n with 2
f(2) = f(1) - 4
f(2) = 4-4 ... replace f(1) with 4
f(2) = 0
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Repeat for n = 3
f(n) = f(n-1)-4
f(3) = f(3-1)-4
f(3) = f(2) - 4
f(3) = 0 - 4 .... replace f(2) with 0, which is from f(2) = 0 found earlier
f(3) = -4
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Repeat for n = 4
f(n) = f(n-1)-4
f(4) = f(4-1)-4
f(4) = f(3) - 4
f(4) = -4-4 ... plug in f(3) = -4
f(4) = -8
