Question

$t ^{2} - 15$

Answer 1

t²-15
$(t + \sqrt{15} )(t - \sqrt{15} )$
= t=- root 15 and t=+ root 15

Answer 2

$\tt \large Hye!!! \:$

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${t}^{2} - 15= 0 \\ \\ {t}^{2} = + 15\\ \\ t = \sqrt{15}$

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