Which of the following relations is not a function

a.) (5,5), (-6,2), (5,1), (8,6)
b.) (-8,4), (4,3), (-5,1), (7,2)
c.) (9,5), (-6,2), (6,1), (-8,2)
d.) (-4,6), (4,-6), (2,0), (0,1)

Which of the following parabolas opens down?

Thanh and her crew are building a stage in the shape of a trapezoid for an upcoming festival. the lengths of the parallel sides of the trapezoid are 14 ft and 24 ft. the height of the trapezoid is 12 ft. what is the area of the stage? enter your answer in the box. ft²

The power generated by an electrical circuit (in watts) as a function of its current c (in amperes) is modeled by p(c)= -15c(c-8) what current will produce the maximum power?