
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 point G is the centroid of triangle ABC, with the sides opposite to angles A, B, and C being of lengths a, b, and c respectively, and $$\frac {a}{5} \overrightarrow {GA}+ \frac {b}{7} \overrightarrow {GB}+ \frac {c}{8} \overrightarrow {GC}= \overrightarrow {0}$$, then the size of angle B is \_\_\_\_\_\_.

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