Let's simplify the expression:

(1 - cos a + cos^2 a) / (sin a - sin^2 a)

Since cos^2 a = 1 - sin^2 a, we can rewrite the expression as:

(1 - cos a + 1 - sin^2 a) / (sin a - sin^2 a)

Simplify the numerator:

(2 - cos a - sin^2 a) / (sin a - sin^2 a)

Now, we can factor out a negative sign from the numerator:

-(cos a + sin^2 a - 2) / (sin a - sin^2 a)

At this point, we can't simplify the expression any further.