$(3 x+7)(3 x-7)$

Step 1 ：Multiply the binomials using FOIL method: \((3x+7)(3x-7) = 3x(3x) + 3x(-7) + 7(3x) + 7(-7)\)

Step 2 ：Combine like terms: \(9x^2 - 21x + 21x - 49 = 9x^2 - 49\)

Step 3 ：Final Answer: \(\boxed{9x^2 - 49}\)