Evaluate
-\left(a-b\right)^{2}+81
Expand
81-b^{2}+2ab-a^{2}
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81-\left(a^{2}-2ab+b^{2}\right)
Use binomial theorem \left(p-q\right)^{2}=p^{2}-2pq+q^{2} to expand \left(a-b\right)^{2}.
81-a^{2}+2ab-b^{2}
To find the opposite of a^{2}-2ab+b^{2}, find the opposite of each term.
81-\left(a^{2}-2ab+b^{2}\right)
Use binomial theorem \left(p-q\right)^{2}=p^{2}-2pq+q^{2} to expand \left(a-b\right)^{2}.
81-a^{2}+2ab-b^{2}
To find the opposite of a^{2}-2ab+b^{2}, find the opposite of each term.
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