Resposta :
f(x) = 3x+1
f(9) = 3.9 + 1 f(1) = 3.1 + 1
f(9) = 24 + 1 f(1) = 3 + 1
f(9) = 25 f(1) = 4
f(9) - f(1) = 25 - 4
f(9) - f(1) = 21
f(9) = 3.9 + 1 f(1) = 3.1 + 1
f(9) = 24 + 1 f(1) = 3 + 1
f(9) = 25 f(1) = 4
f(9) - f(1) = 25 - 4
f(9) - f(1) = 21