Answers:
Functions
- y = -x+11
- y = 2x^2-6x+4
- y = -7
Not functions
- x = 3
- x^2+y^2 = 81
- y^2 = -5x-12
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Step-by-step explanation:
A function is possible if and only if any given x input leads to exactly one y output.
For something like x^2+y^2 = 81, we can see that x = 0 leads to either y = 9 or y = -9. So this would not be a function. We would need x to pair with only y value to have it be a function.
We have the same thing going on with y^2 = -5x-12 as well.
For anything of the form x = k, where k is any real number, this is also not a function. We have one single input only and it leads to infinitely many outputs. So in a sense, this is even worse compared to the other examples.
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In summary, we have these three non-functions:
- x = 3
- x^2+y^2 = 81
- y^2 = -5x-12
Everything else is a function. You can use the vertical line test as a visual way to check.