
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 an ellipse with the equation $\frac{x^{2}}{a^{2}}+ \frac{y^{2}}{b^{2}}=1 (a > b > 0)$, its eccentricity is $\frac{\sqrt{3}}{2}$, the right focus is $F$, and the endpoints of the minor axis are $B_{1}$ and $B_{2}$. Additionally, $\overrightarrow{FB_{1}} \cdot \overrightarrow{FB_{2}}=4$.
(1) Find the equation of the ellipse;
(2) A line $l$ passes through the point $M(0,-1)$, intersecting the ellipse at points $A$ and $B$, and intersecting the $x$-axis at point $N$, such that $\overrightarrow{NA}=- \frac{7}{5} \overrightarrow{NB}$. Find the equation of the line $l$.

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