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If the value of determinant `|[m,2],[-5,7]|`is 31, find the value of m

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#### Solution

`|[m,2],[-5,7]|=31`

∴(m × 7) – (–5 × 2) = 31

∴7m – (–10) = 31

∴7m + 10 = 31

∴7m = 21

∴m = 3

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