
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 points P and Q are two fixed points on the plane of $\triangle ABC$, and it satisfies $\overrightarrow {PA}+ \overrightarrow {PC}= \overrightarrow {0}$, $2\overrightarrow {QA}+ \overrightarrow {QB}+ \overrightarrow {QC}= \overrightarrow {BC}$. If $|\overrightarrow {PQ}|=λ|\overrightarrow {BC}|$, then the positive real number $λ=$ ______.

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