Note that the function value under the radical canot be less than zero
Set this equal to 0
-10x^2 -11x + 6 = 0 multiply through by -1
10x^2 + 11x - 6 = 0 factor
(5x - 2)(2x + 3) = 0 set each factor to 0 and we solve for x
This gives that x = 2/5 and x = -3/2
The answer comes from these two intervals (-inf, -3/2) U (2/5, inf) or from the interval [-3/2, 2/5]
And in the original function, the domain of [-3/2, 2/5 ] will make the quantity under the radical greater than or equal to 0