Given the function f (x) = sin (x + π / 6), where x ∈ [- π / 3, a], if the range of F (x) is [- 1 / 2,1], then the range of a is

Given the function f (x) = sin (x + π / 6), where x ∈ [- π / 3, a], if the range of F (x) is [- 1 / 2,1], then the range of a is

From - π / 3 ≤ x ≤ a,
There are - π / 6 ≤ x + π / 6 ≤ a + π / 6
Let t = x + π / 6, as shown in the figure,
And the range of y = Sint is [- 1 / 2,1],
π/2≤t≤7π/6
That is, π / 2 ≤ a + π / 6 ≤ 7 π / 6
The solution is π / 3 ≤ a ≤ π
So the value range of a is [π / 3, π]