### Solving equation with sqrt

Hello!

I'm trying to solve the following equation:

sage: var('a b c')
(a, b, c)
sage: a==b-sqrt(b**2-c**2/4)
a == b - sqrt(b^2 - 1/4*c^2)
sage: solve(_, b)
[b == a + sqrt(b^2 - 1/4*c^2)]

In the last line Sage doesn't solve the equation for b completely. Can you give me a hint what I'm doing wrong?
Thank you!