f(x) = − √ 2 − x^2

Solve for x:
-sqrt(2)-x^2 = 0

Add sqrt(2) to both sides:
-x^2 = sqrt(2)

Multiply both sides by -1:
x^2 = -sqrt(2)

Take the square root of both sides:
Answer: | 
| x = i2^(1/4)        or               x = -i2^(1/4)

Guest, I am wondering why you put this function equal to zero?   There is no =0 in the question.     :///

f(x) = − √ 2 − x^2

There is no question here at all !