Question

$log_{4} ( {x}^{2} - 15x) = 2$
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Answer 1

Ответ:

$log_{4}( {x}^{2} - 15 x) = 2 \\ {x}^{2} - 15x = {4}^{2} \\ {x}^{2} - 15x - 16 = 0 \\ \\ d = {b}^{2} - 4ac = 225 + 4 \times 16 = 289 = {17}^{2} \\ \\ x1 = \frac{ - b - \sqrt{d} }{2a} = \frac{15 - 17}{2} = 1 \\ \\ x2 = \frac{ - b + \sqrt{d} }{2a} = \frac{15 + 17}{2} = 16$

Ответ -1 и 16