Mathematica partial differentiation weirdness

[kahwawashay1]

I am checking my homework with mathematica, but sometimes when I write stuff like
D[(x/((x^2 - y^2)^0.5)), y] , which is supposed to give me the partial derivative of x/((x^2 - y^2)^0.5) with respect to y, i get answer like:

(1. x y)/(x^2 - y^2)^1.5

which is right, except for the random "1."

as another example, when I differentiate above function with respect to x, I again get an answer with "1.x^2" in a numerator.

what on Earth is this "1." ?

 

[lurflurf]

1x=x

In this case the 1. means that the answer is approximate, as your .5 is approximate.

D[(x/((x^2 - y^2)^a)), y] =(2a x y)/(x^2 - y^2)^(a+1)

if a=1/2
2a=1
a+1=1.5

if it is only approximately true
a=.5
2a=1.
1+a=1.5