
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 that $α∈( \dfrac {π}{2},π)$, and $\sin \dfrac {α}{2}+\cos \dfrac {α}{2}= \dfrac {2 \sqrt {3}}{3}$.
(1) Find the values of $\sin α$ and $\cos α$;
(2) If $\sin (α+β)=- \dfrac {3}{5},β∈(0, \dfrac {π}{2})$, find the value of $\sin β$.

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