Упростите выражение упростить

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Подкоренное выражение корня чётной степени должно быть ≥ 0.
1) x + 1 ≥ 0                        2)  9 - x² ≥ 0
    x ≥ - 1                                 x² - 9 ≤ 0
                                               (x - 3)(x + 3) ≤ 0
                                                   +                 -                     +
                                              __________________________
                                                           - 3      - 1              3
                                                                      //////////////////////////////
Область определения : x ∈ [ - 1 ; 3]

Possible derivation:
d/dx(y) = d/dx(1/2 cos(2 x)-x)
The derivative of y is zero:
0 = d/dx(-x+1/2 cos(2 x))
Differentiate the sum term by term and factor out constants:
0 = (d/dx(cos(2 x)))/2-d/dx(x)
The derivative of x is 1:
0 = 1/2 (d/dx(cos(2 x)))-1
Using the chain rule, d/dx(cos(2 x)) = ( dcos(u))/( du) ( du)/( dx), where u = 2 x and ( d)/( du)(cos(u)) = -sin(u):
0 = -1+1/2-d/dx(2 x) sin(2 x)
Factor out constants:
0 = -1-1/2 sin(2 x) 2 d/dx(x)
Simplify the expression:
0 = -1-(d/dx(x)) sin(2 x)
The derivative of x is 1:
Answer: |
| 0 = -1-1 sin(2 x)