
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
In $\triangle ABC$, $\angle A=90^{\circ}$, $AB=1$, $BC= \sqrt {5}$, point $M$ and $N$ satisfy $\overrightarrow{AM}=λ \overrightarrow{AB}$, $\overrightarrow{AN}=(1-λ) \overrightarrow{AC}$, $λ∈R$, if $\overrightarrow{BN}\cdot \overrightarrow{CM}=-2$, then $λ=$ _____ .

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