Because x – sqrt(x) – 9 is not an equation and therefore cannot be solved. x – sqrt(x) – 9 is an expression. Expressions cannot be solved; they can only be simplified.

I’ll assume you mean x – sqrt(x) – 9 = 0

Let y = sqrt(x), then y^2 = x

The equation becomes

y^2 -y -9 = 0

Now use the quadratic formula.

y = [-b +/- sqrt(b^2 -4ac)] / (2a)

a = 1, b = -1, and c = -9

y = [1 +/- sqrt((-9)^2 -4(1)(-9))] / (2*1)

y = [1 +/- sqrt(81 +36)] / 2

y = [1 +/- sqrt(117)] / 2

y = [1 +/- sqrt(9*13)] / 2

y = [1 +/- 3 sqrt(13)] / 2

y = [1 + 3sqrt(13)]/2 or y = [1 -3sqrt(13)]/2

Recall that y = sqrt(x), so you will need to square y in order to find x.