Cho hàm số Y = f(x) = 2004x.

a) Chứng minh f(a + b) = f(a) + f(b).

b) Tìm x để f(x) = x².

a) Ta cos: f(a) = 2004a; f(b) = 2004b

f(a + b) = 2004(a + b)

f(a) + f(b) = 2004a+ 2004b = 2004(a + b)

Suy ra: f(a + b) = f(a) + f(b)

b) f(x) = x²

Suy ra: 2004x = x²

⇒ x² – 2004x = 0

⇔ x(x – 2004) = 0

⇔ \(\left[ \begin{array}{l}x = 0\\x = 2004\end{array} \right.\).