
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]


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Given two vectors $\overrightarrow {a}$ and $\overrightarrow {b}$ in a plane, with $|\overrightarrow {a}|=3$ and $|\overrightarrow {b}|=2$, and satisfying $(\overrightarrow {a}+\overrightarrow {b})(\overrightarrow {a}-2\overrightarrow {b})=4$, find the angle between the vectors $\overrightarrow {a}$ and $\overrightarrow {b}$ (in radians).

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