For what value of the constant c is the function f continuous on (-∞, ∞)?
f(x) =
cx^2 + 3x if x < 4
x^3 - cx if x ≥ 4
Note that f is continuous on (-∞, 4) and (4, ∞). For the function to be continuous on (-∞, ∞), we need to ensure that as x approaches 4, the left and right limits match.
First, we find the left limit.
lim x→4- f(x) = lim x→4- (cx^2 + 3x) = 16c + 12
Next, we find the right limit.
lim x→4+ f(x) = lim x→4+ (x^3 - cx) = _________