f(x - y) = f(x) - f(y), f(12) = 16, f(3) = ? https://scontent-vie1-1.xx.fbcdn.ne...=8e6f11a7fe71f47ba3ad9cca34ac5b9b&oe=5D4F483D https://www.facebook.com/photo.php?fbid=643831326059305&set=g.1174585619345646&type=1&theater&ifg=1 f(a) = k·a f(x) = k·x f(y) = k·y f(x - y) = k(x - y) k(12) = 16 ⇒ k = 4 / 3 f(a) = 4a / 3 f(3) = 4·3 / 3 = 4