Question

Which equation does not represent a function?


A)
y = 2x + 3


B)
x = 4y + 7


C)
x2 = -2y + 1


D)
y2 = -5x - 8

Answer 1

The one in which two different y values give the same x value.

Answer 2

so we have to put it in slope intercept form to get the y value? I'm so confused

Answer 3

The given equations are not all lines so they cannot all be put in slope-intercept form.

Answer 4

so what form do I put it in?

Answer 5

Solve for y..

Answer 6

C?

Answer 7

its either c or D

Answer 8

wait..... What values do we substitute for y?

Answer 9

You could resort to just looking at the equations and thinking something like this:
For the first equation, y = 2x+3, replace y with 1 and you get -1 for x. Replace y with -1 and you get -2 for x. Different y, different x.

Answer 10

Now try that with the last equation, y^2=-5x-8.
Replace y with 1 and you get -9/5 for x
Replace y with -1 and you get -9/5 for x
That cannot be a function because now you have two ordered pairs with the same first number.

Answer 11

One more hint.. A function must produce a unique y value for each x. But when we take square root, there are two possible (real) roots + or - of the value.

Answer 12

so it's d because the 2 y values equal the same x value?

Answer 13

Exactly.

Answer 14

ohhhhh ok thanks guys :)

Answer 15

yw

Answer 16

i have to take my eoc next week and i have a bunch of practice stuff to do

Answer 17

Keep working hard and you'll be fine.

Answer 18

:)