Which relationship shows a quadratic variation?

x| 2 | 3 | 4 | 5 |
f(x) |1 |4 | 9 | 16|

x| 1 | 2 | 3 | 4 |
f(x) |2 |8 | 18 | 32|

x| 1 | 2 | 3 | 4 |
f(x) |2 | 5 | 10 | 17|

x| 1 | 2 | 3 | 4 |
f(x)| 4 | 3 | 2 | 1 |

Question

Which relationship shows a quadratic variation?
 
    x| 2 | 3 | 4 | 5 |
f(x) |1 |4 | 9 | 16| 

     x| 1 | 2 | 3 | 4 |
f(x) |2 |8 | 18 | 32| 

    x| 1 | 2 | 3 | 4 |
f(x) |2 | 5 | 10 | 17| 

 x| 1 | 2 | 3 | 4 |
 f(x)| 4 | 3 | 2 | 1 |

bananas1234 · Answer

@Nnesha I'm not sure what to do on this one......

bananas1234 · Answer

@Directrix could you help me?

nnesha · Answer

do you know da equation for quadratic variation ?

bananas1234 · Answer

f(x) = kx squared

ribhu · Answer

3rd relationship
fx = x^2 +1

ganeshie8 · Answer

Im inclining toward second option : 
$$f(x) = 2x^2$$

nnesha · Answer

yes because equation for quadratic equation is $$\huge\rm y = kx^2$$
 first find k
for 2nd choice

bananas1234 · Answer

ok

nnesha · Answer

|dw:1424321010263:dw|
if we use first two points 
(1,2) we get  k = 2