Which relation is a function? a. {(1, 2), (2, 3), (3,  2), (2, 1)} b. {(4, 2), (3, 3), (2,  4), (3, 2)} c. {(1, −1), (−2, 2), (−1,  2), (1, −2)} d. {(1, 4), (2, 3), (3,  2), (4, 1)}

D

Step-by-step explanation:

A relation is a set of related points. A function is a set of related points where no inputs repeat.

A. {(1, 2), (2, 3), (3,  2), (2, 1)}

This repeats (2,3) and (2,1). Not a function.

​B. {(4, 2), (3, 3), (2,  4), (3, 2)}  

This repeats (3,3) and (3,2). Not a function.

C. {(1, −1), (−2, 2), (−1,  2), (1, −2)}

This repeats (1,-1) and (1,-2). Not a function.

D. {(1, 4), (2, 3), (3,  2), (4, 1)}

This doe NOT repeat. Function.

step-by-step explanation: yes

answer:

a=9

step-by-step explanation: lmk if you need a explanation