
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 $\overrightarrow{a}=( \sqrt {3}\sin 2x+3,\cos x)$ and $\overrightarrow{b}=(1,2\cos x)$, let the function $f(x)= \overrightarrow{a}\cdot \overrightarrow{b}$  
$(1)$ Find the smallest positive period of the function $f(x)$ and the center of symmetry of its graph;  
$(2)$ When $x\in\left[ \frac {\pi}{12}, \frac {7\pi}{12}\right]$, find the range of the function $f(x)$.

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