hello,

i have this

in triangle ABC, AB=(5-x) BC=(4+x) , angle ABC = 120 degrees and AC = y

i know that $\displaystyle y^2=x^2 - x + 61$

now i have to complete the square to find minimum value of y^2 and give value of x for which this occurs

but i cant figure out how to start with it, because there is no roots