Evaluate
21-12x-9x^{2}
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21-12x-9x^{2}
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25-\left(9x^{2}+12x+4\right)
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(3x+2\right)^{2}.
25-9x^{2}-12x-4
To find the opposite of 9x^{2}+12x+4, find the opposite of each term.
21-9x^{2}-12x
Subtract 4 from 25 to get 21.
25-\left(9x^{2}+12x+4\right)
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(3x+2\right)^{2}.
25-9x^{2}-12x-4
To find the opposite of 9x^{2}+12x+4, find the opposite of each term.
21-9x^{2}-12x
Subtract 4 from 25 to get 21.
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