This is the boss. No calculator: the function is three lines, a square plus a constant on the left, a lone value at the boundary, a line on the right, and every number is small enough to hold in your head. One function, one long inspection, and every answer feeds the next: evaluate each piece where it lives, take the left-hand limit from the first line and the right-hand limit from the third, compare them with the lone value in the middle, name the verdict, and then say what single value would mend the gap.

Everything in the chapter rides in here: which line owns the boundary, a limit that ignores $f(c)$, the three conditions, and the difference between a hole you can fill and a jump you cannot. Write each line down as you go; a slip in line two walks all the way to line seven. 5★ under par is the chapter crown.