20. For the limit to exist the left and right approaches to 3 must be equal.

Limit for x➝3⁻ is 2 but the limit for x➝3⁺ is 3. So the limit for x➝3 is undefined.

21. For x➝2⁻ the limit is 2 and for x➝2⁺ the limit is 6-2=4. Because the left and right limits are unequal the limit for x➝2 is undefined.

22. For x➝2⁻ limit is 3, for x➝2⁺ limit is 4 so the left and right limits are different and for x➝2 the limit is undefined (same as doesn’t exist).

23. Lim(f)-lim(g)=L-M=lim(f-g) because we can write h(x)=f(x)-g(x) reducing f-g to a single function. Since the limit for both f and g is for x➝a, then it also applies for h(x) for x➝a.