
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 universal set $U=\mathbb{R}$, let the set $A=\{x|x^{2}-3x-18\geqslant 0\}$, and $B=\{x| \frac {x+5}{x-14}\leqslant 0\}$.  
$(1)$ Find $(\complement_{U}B)\cap A$.  
$(2)$ If the set $C=\{x|2a < x < a+1\}$, and $B\cap C=C$, find the range of the real number $a$.

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