If $81$ is the discriminant of $2 x^{2} + 5 x - k = 0$ , then the value of $k$ is

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Solution

Finding the value of $k$ :
Given expression : $2 x^{2} + 5 x - k$
$D = b^{2} - 4 a c$ $= 81$
$a = 2, b = 5, c = - k; 5^{2} - 4 \times 2 (- k) = 81; 25 + 8 k = 81 8 k = 56 k = 7$
Hence the value of $k = 7$ .

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