Hey Tutu.

Try using the fact that SQRT(x)*SQRT(1-x) = SQRT(x - x^2) and then complete the square.

Hint: Completing the square for ax^2 + bx is adding the term (0.5*b/SQRT(a))^2 and also -(0.5*b/SQRT(a))^2 to get (SQRT(a)*x + 0.5*b/SQRT(a))^2 - (0.5*b/SQRT(a))^2.