
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
It is known that the vertex of angle $\theta$ is at the origin of coordinates, its initial side coincides with the positive half-axis of the x-axis, and its terminal side falls on the ray $y= \frac {1}{2}x$ ($x\leq0$).  
(Ⅰ) Find the value of $\cos\left( \frac {\pi}{2}+\theta \right)$;  
(Ⅱ) If $\cos\left( \alpha+ \frac {\pi}{4} \right)=\sin\theta$, find the value of $\sin\left(2\alpha+ \frac {\pi}{4}\right)$.

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