The function f (x) = 2Sin [(1 / 3) x + a] x belongs to R, - Wu / 2

The function f (x) = 2Sin [(1 / 3) x + a] x belongs to R, - Wu / 2

Since m (- π, - 2) is on the image, the coordinate of M is substituted into the analytic expression
-2=2sin(-π/3+A)
sin(-π/3+A)=-1
So - π / 3 + a = 3 π / 2 + 2K π, K ∈ Z
Then a = 11 π / 6 + 2K π, K ∈ Z
Because - π / 2