Which of the following expressions represents a function?

a) x^2 + y^2 = 9
b) {(4, 2), (4, –2), (9, 3), (9, –3)}
c) x = 4
d) 2x + y = 5

In the image, point a marks the center of the circle. which two lengths must form a ratio of 1 : 2? (options are in the images since thought they were harmful phrases)

Lance lived in portugal and brazil for a total of 14 months to learn portuguese. he learned an average of 130 new words per month when he lived in portugal, and an average of 150 new words per month when he lived in brazil. in total he learned 1920 new words. write a system of equations to represent the situation. use x to represent portugal, and y to represent brazil

If the sales price of a dvd is $20 and the markup is 34%, what is the cost of the dvd?