Since we can't take the square root of a negative quantity, we need to find where -10x^2 - 11x + 6 = 0
Set it = 0 and multiply through by a -1....so we have
10x^2 + 11x - 6 = 0 factor, if possible
(5x - 2)(2x + 3) = 0
Setting each to 0, we have that x = 2/5 and x = -3/2
Now, we need to find the intervals where -10x^2 - 11x + 6 < 0
This will occur at either x < -3/2 or -3/2 < x < 2/5 or x > 2/5
Letting x = 0 we see that -3/2 < x < 2/5 "works"
If you pick any point in the other two intervals, the expression inside the radical will be < 0.
So, our answer is -3/2 ≤ x ≤ 2/5
Here's a graph of the function that confirms our answer.....https://www.desmos.com/calculator/lhjgwiihyv