
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 vertex of angle α coincides with the origin O, its initial side coincides with the non-negative semi-axis of the x-axis, and its terminal side passes through point P ($$- \frac {3}{5}， \frac {4}{5}$$).
(Ⅰ) Find the value of sin(α+π);
(Ⅱ) If acute angle β satisfies sin(α+β) = $$\frac {5}{13}$$, find the value of cosβ.

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