
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 $\overrightarrow{e_{1}}, \overrightarrow{e_{2}}$ are a pair of basis vectors on a plane,
(1) Given $\overrightarrow{AB}=2 \overrightarrow{e_{1}}+ \overrightarrow{e_{2}}$, $\overrightarrow{BE}=- \overrightarrow{e_{1}}+λ \overrightarrow{e_{2}}$, $\overrightarrow{EC}=-2 \overrightarrow{e_{1}}+ \overrightarrow{e_{2}}$, and points $A$, $E$, $C$ are collinear, find the value of the real number $λ$;
(2) If $\overrightarrow{e_{1}}, \overrightarrow{e_{2}}$ are unit vectors with an angle of $60^{\circ}$ between them, $\overrightarrow{a}= \overrightarrow{e_{1}}+λ \overrightarrow{e_{2}}$, $\overrightarrow{b}=-2λ \overrightarrow{e_{1}}- \overrightarrow{e_{2}}$, find the maximum and minimum values of $\overrightarrow{a}\cdot \overrightarrow{b}$ when $-3\leqslant λ\leqslant 5$.

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