Part 1.
A. x=0 can be used for function that have x≤1, so f(x) =x²
B.You need substitute x by 0. x=0,
then
f(0) = 1) x² =0² =0 x≤1
Part 2.
A. f(x) =x², Graph is attached.
B. f(x) =2x+1, Graph is attached.
C. The functions will change in the point x=1
For f(x) =x² , x ≤1 ; f(1) = 1. The point (1,1) is included, the dot should be filled (closed).
For the function f(x)=2x+1, x>1. The point f(1)=3 is not included, the dot should be empty(open).
D. Point(1,1) is closed(filled circle), point (1,3) is open(empty circle).