# Which one isn't a function?

#### melissax

##### New member
Hi, I have a question and couldnt solve.
Can you help me?
Which one isnt function how i can show?

(a) y = |x^3 + 5|
(b) y = x2 + sqrt(x) -sin(x)
(c) y2 = (x-5)^2 + 10
(d) y3 = x + 4

Thank you?

#### Opalg

##### MHB Oldtimer
Staff member
Re: Which one isnt function?

Hi, I have a question and couldnt solve.
Can you help me?
Which one isnt function how i can show?

(a) $y = |x^3 + 5|$
(b) $y = x^2 + \sqrt(x) -\sin(x)$
(c) $y^2 = (x-5)^2 + 10$
(d) $y^3 = x + 4$

Thank you?
The essential thing about a function is that there should be only one value of $y$ for each value of $x$. Can you see one of those formulas where there might be more than one value of $y$ for a given value of $x$?

#### Mr Fantastic

##### Member
Re: Which one isnt function?

Hi, I have a question and couldnt solve.
Can you help me?
Which one isnt function how i can show?

(a) y = |x^3 + 5|
(b) y = x2 + sqrt(x) -sin(x)
(c) y2 = (x-5)^2 + 10
(d) y3 = x + 4

Thank you?
You should have been taught the 'vertical line test' .....

#### melissax

##### New member
Re: Which one isnt function?

should i give value to the x?

If i give can i understan is function or not?

#### MarkFL

If the given relation can be expressed as $\displaystyle y=f(x)$, then it is a function. Only one of the given relations cannot be written this way.