
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 the angle between vectors $\overrightarrow {AB}$ and $\overrightarrow {AC}$ is 120°, and $|\overrightarrow {AB}|=2$, $|\overrightarrow {AC}|=3$. If $\overrightarrow {AP} = \lambda \overrightarrow {AB} + \overrightarrow {AC}$, and $\overrightarrow {AP} \perp \overrightarrow {BC}$, then the value of the real number $\lambda$ is ______.

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