
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 $\overrightarrow{a}=(\cos α,\sin α)$ and $\overrightarrow{b}=(\cos β,\sin β)(0 < α < \dfrac {π}{2}\,,\,- \dfrac {π}{2} < β < 0)$ with $|\overrightarrow{a}- \overrightarrow{b}|= \dfrac {2 \sqrt {5}}{5}$,
(I) find the value of $\cos (α-β)$;
(II) if $\cos β= \dfrac {12}{13}$, find the value of $\cos α$.

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