Evaluate
\left(2x+9\right)^{2}-72
Expand
4x^{2}+36x+9
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4x^{2}+36x+81-72
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(2x+9\right)^{2}.
4x^{2}+36x+9
Subtract 72 from 81 to get 9.
4x^{2}+36x+81-72
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(2x+9\right)^{2}.
4x^{2}+36x+9
Subtract 72 from 81 to get 9.
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