
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 $O$ is the origin of coordinates, and the parabola $C$: $y^{2}=nx(n > 0)$ has a point $P(2,t)$ in the first quadrant whose distance to the focus is $\dfrac {5}{2}$. The tangent line to curve $C$ at point $P$ intersects the $x$-axis at point $Q$. A line $l_{1}$ passes through point $Q$ and is perpendicular to the $x$-axis.  
(Ⅰ) Find the length of segment $OQ$;  
(Ⅱ) Suppose a moving line $l_{2}$: $x=my+b$ that does not pass through points $P$ and $Q$ intersects curve $C$ at points $A$ and $B$, and intersects $l_{1}$ at point $E$. If the slopes of lines $PA$, $PE$, $PB$ form an arithmetic sequence in order, does $l_{2}$ pass through a fixed point? Please explain your reasoning.

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