
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 the ellipse $\frac {x^{2}}{a^{2}}+ \frac {y^{2}}{b^{2}}=1$ with a major axis length of 4, and the minor axis length is half of the major axis length.
(1) Find the equation of the ellipse;
(2) A line $l$ passes through point M(2,1) and intersects the ellipse at points A and B. If M is the midpoint of segment AB, find the equation of line $l$.

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