
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given the function $f(x)= \sqrt {3}\sin (ωx+φ)(ω > 0,- \frac {π}{2}\leqslant φ < \frac {π}{2})$, $f(0)=- \frac { \sqrt {3}}{2}$, and the minimum distance between any two symmetry axes on the graph of the function $f(x)$ is $\frac {π}{2}$.
(I) Find the analytic expression of the function $f(x)$;
(II) If $f( \frac {α}{2})= \frac { \sqrt {3}}{4}( \frac {π}{6} < α < \frac {2π}{3})$, find the value of $\cos (α+ \frac {3π}{2})$.

Present the answer in LaTex format: \boxed{Your answer}
user