1. The problem statement, all variables and given/known data Find any critical point of the following function. f(t)= 3 — lt-3l, [-1,5] The answer says it has a critical point where t=3. 2. Relevant equations 3. The attempt at a solution f(t)=3 — lt-3l f(t)=3-t+3, t≥3 f'(t)= -1 f(t)=3-(-t+3), t<3 f'(t) = 1 The function is not differentiable. And it has no critical point. Two cases have different values -> my answer I remember the definition of critical point is where the derivative of the function either is zero or doesn't exist. What did I do wrong? and Why is t=3 a critical point? Thanks.