Select the sets that are not functions.
a = {(1, 2), (2, 3), (3, 4), (4, 5)}
b = {(1, 2), (2, 1), (3, 0), (4, -1)}
c = [(-1, 3), (0, 3), (1, 3), (2, 3)}
d = {(1, 1), (1, 2), (1, 3), (1, 4);
e = {(6,2), (7,3), (6,-1), (5,4)}

D,E are not functions

Step-by-step explanation:

A function is a relation in which every  input has not more than one output.But the output of the inputs may be same.Here in D the input 1 has 4 different outputs as 1,2,3,4.So its not a function.Similarly in E 6 has 2 outputs as 2 and -1.For remaining sets the inputs has only one output.so they are functions.

a28=58

step-by-step explanation:

a1=a1+(n-1)d

a28= 4+ (28-1)2

a28=4+(27)(2)

a28=4+54

a28=58