If $l = - 1$ and $m = 2$ , then the value of $4 l^{2} + 9 m^{2} + 2 l m - 9 l^{2} m$ is ______.

39

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24

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18

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36

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Solution

The correct option is C $18$
We have, $4 l^{2} + 9 m^{2} + 2 l m - 9 l^{2} m$
= $4 ({- 1}^{2}) + 9 (2^{2}) + 2 (- 1) (2) - 9 ({- 1}^{2}) (2)$
= 4 + 36 - 4 - 18
= 40 - 22 = 18

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