By definition, a function is odd if f(-x) = -f(x) for all x in the domain. The answer is choice C
Side note: a function is even if f(-x) = f(x) for all x in the domain
I don't either it is quite hard to be fair
The distance formula is:

We are given two points in the form (x,y), so plug in the values to the distance formula:

Next we can simplify. We know that 12-12 is 0, so we can drop it from the equation, as it will not affect our answer. Also, we know that -10-15 is -25:

The square and square root cancel each other out leaving us with 25.
The answer is 25.
Tan 2 pi/3= (sin2pi/3)/(cos2pi/3)= (sqrt 3)/2 dividend by (-1/2)= - sqrt 3