No it isn't.
Explanation:
x/y * y = (y-6) * y
x = y^2 - 6y
A function gives just one y for every x
In this case there will always be 2 y's for every x
Example:
y can be
y = 6
or
y =−6
(0,-6) & (0,6)
You need Pythagorean theorem for this.
a² + b² = c², where c is the hypotheneus and a and b are the sides of the right triangle.
24² + x² = 26²
x² = 676-576
x = ±√100
x = 10 (-10 is rejected because length of triangle cannot be a negative number)
If you keep simplifying it would end up to 4/21