Question

O valor correspondente ao produto dos zeros da função y = - x² + 7x - 10 é: *

a) 10
b) 9
c) - 10
d) - 9
e) 3

Answer 1

$\Delta = b^2-4ac\\\Delta = 7^2 - 4 \mbox{ } . (-1) \mbox{ } . \mbox{ } (-10)\\\Delta = 49 - 40\\\Delta = 9\\\\\displaystyle x=\frac{-b\mbox{ }\pm\mbox{ }\sqrt{\Delta}}{2a}\\\\\displaystyle x=\frac{-7\mbox{ }\pm\mbox{ }\sqrt{9}}{2 \mbox{ } . \mbox{ } (-1)}\\\\\displaystyle x=\frac{-7\mbox{ }\pm\mbox{ }3}{-2}\\\\x' = \frac{-7+3}{-2} = \frac{-4}{-2}=2\\\\x'' = \frac{-7-3}{-2} = \frac{-10}{-2} = 5\\\\\\x' + x'' = 2\mbox{ } . \mbox{ }5 = 10$