Evaluate
-\left(a-18\right)\left(a+12\right)
Expand
216+6a-a^{2}
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225-\left(a^{2}-6a+9\right)
Use binomial theorem \left(p-q\right)^{2}=p^{2}-2pq+q^{2} to expand \left(a-3\right)^{2}.
225-a^{2}+6a-9
To find the opposite of a^{2}-6a+9, find the opposite of each term.
216-a^{2}+6a
Subtract 9 from 225 to get 216.
225-\left(a^{2}-6a+9\right)
Use binomial theorem \left(p-q\right)^{2}=p^{2}-2pq+q^{2} to expand \left(a-3\right)^{2}.
225-a^{2}+6a-9
To find the opposite of a^{2}-6a+9, find the opposite of each term.
216-a^{2}+6a
Subtract 9 from 225 to get 216.
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