Question

find the missing number:12+85/?=?

Answer 1

12 + 85/x = x

12 = x - 85 / x

$12 =( x {}^{2} - 85) \div x$
$x {}^{2} - 12x - 85 = 0$

$x {}^{2} - 17x + 5x - 85 = 0$

$x(x - 17) + 5( x - 17) = 0$

$(x + 5)(x - 17) = 0$

$x = - 5 \: \: \:a nd \: \: 17$


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