
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 vectors $\overrightarrow{a}=(1,\cos 2x)$, $\overrightarrow{b}=(\sin 2x,- \sqrt {3})$, and the function $f(x)= \overrightarrow{a}\cdot \overrightarrow{b}$.
(I) If $f( \frac {θ}{2}+ \frac {2π}{3})= \frac {6}{5}$, find the value of $\cos 2θ$;
(II) If $x\in[0, \frac {π}{2}]$, find the range of the function $f(x)$.

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