Question

Determine, se existirem, os zeros da função f(x) = -x² +2x + 8 ?

Answer 1

$-x^2 + 2x + 8 = 0\\\Delta = 2^2 - 4 \cdot (-1) \cdot 8\\\Delta = 4 + 4 \cdot 8\\\Delta = 4 + 32\\\Delta = 36\\\\x = \frac{-2\pm \sqrt{36}}{2 \cdot (-1)} = \frac{2\pm6}{2} = 1 \pm 3\\\\x_1 = 1 + 3 = 4\\x_2 = 1 - 3 = -2\\\\\boxed{S = \{-2, \ 4\}}$