Question 12***+Explain why the factor \(h\) must be cancelled before setting \(h=0\) in a first-principles derivative.
Question 16****+Use first principles to find \(f'(0)\) for \(f(x)=|x|\), or explain why it does not exist.
Question 18*****A student substitutes \(h=0\) into \(\frac{(x+h)^2-x^2}{h}\) and says the derivative is undefined. Diagnose the error.
Question 19*****Use first principles to show that the derivative of a constant function \(f(x)=c\) is zero.
Question 20*****Using first principles, explain why a corner in a graph can prevent differentiability.